Nothing survives... out of ideas and about to break this tank down

[TwoTankAmin]

I think you should test the water in the smaller tanks. If there is a notable difference in the parameters between the small and the large, this may explain things. If the fish do fine in the small tanks and die in the big one, there has to be some difference between the two that is fatal. If nothing else it makes sense to rule this out as the potential cause of the problem.

As for copper pipes, old ones are safe but new ones not so. Over time the water builds up a coat on the copper which stops any leaching. A few year back we had some copper piping near the water tanks go bad and need to be replaced. Because I had so many fish which were pretty pricey, I did not take to the idea of replacing copper with copper. It was not a long stretch of pipe so I had them put in Pex which is an alternative to copper.

If there were white patches that could be columnaris. This is a bacterial disease which comes in multiple strains. Some are quite virulent and can wipe out a tank before any symptom are present. Other strains can be way less fatal and a fish can have these strains debilitating the fish but not killing them, at least not quickly, it can take a lot longer. The problem here is that any form of this disease requires antibiotic treatment. And one needs to medicate the entire tank when this is the confirmed problem.

However, there are other things that can create white patches on fish. One of the symprotms of columnaris gives it one of its common names, mouth fungus. You can see what looks to be fungus on the lips of the fish but it is not fungus. This disease is often called saddleback disease because fish often get a white patch at the base of their dorsal fin.

Again, the above is for your consideration as a possibility and not a firm diagnosis. Being able to rule it out eliminates abother possible cause.

Finally, if there is somthing toxic in the tank of which we cannot be aware beyond the fact that the fish keep dying, it makes it difficult to know how to proceed. To remove a contaminant one needs to know what it is, if possible. Changing water may not be enough, even multiple times. While we tend to trust sellers to sell healthy fish and safe decor etc. This is not a guarantee.

There is no way that I can determine that will reveal of there is anything toxic in the tank water. Testing it would cost a fortune. We know it isn't anything in the nitrogen complex. Even that short burst of nitrite is very low and likely not the problem. And if it was, you would definitely see fish gasping at the surface.

 

[mad_tunes]

Just done the JBL tests on of all three tanks and my tap water.
TDS is measured with a cheap electronic meter thingy. I wouldn't give absolute numbers much weight, but it might be useful to roughly compare them.
Didn't do the test strips

Carbonate hardness of the larger tank seems quite low compared to the others.
That has fluctuated a bit, and is at the lower end of its range recently. I'm not sure why that is.

Otherwise, I don't think I see anything very surprising/informative?

 

[AdoraBelle Dearheart]

My heart really goes out to you! Brace yourself for one of my long, waffling, but hopefully helpful posts. Might want to make a cuppa and get comfy!

I've been in a similar situation before, and it's horrible to go through! Can see how much time, money, thought and effort you put into this, the scape is beautiful, and the plants were looking amazing at first. Most of us have been through that excitement of planning a new set up, wanting to stretch your wings a bit, then how heart-breaking it is when things are going wrong! For what it's worth, I don't think you are doing anything obviously "wrong". You're doing all the right things, so don't give up yet! But I can imagine how disheartening this is. You start to think of your lovely planned project as a Tank of Doom!

I'm taking this a bit more personally because your story is so similar to mine - I have a small tank with a colony of breeding pygmies, a larger tank with bronzes and other larger fish, then I bought a 240L Roma hoping to condense the bronzes and another mid-sized tank with guppies and mollies together into the 240, wanting to have one small and one large tank, instead of 3-4 smaller ones. Have a load of sand, stone and decor ready to go, but I haven't got as far as you have yet.

These are just guesses, and what I would do next in your shoes. You've tried different meds and we don't have any real symptoms of disease, and I'm also wondering about potential poisoning sources, and see a few potential suspects I'd want to try to eliminate.

1. The tank itself.
2. The plants
3. The wood, stone or substrate.

1. For the tank itself:
I buy my tanks second hand as well, and have heard a few horror stories about things like copper and other heavy metals from a previous owner medicating the tank or something, remaining attached to the glass and silicone. Usually more of a risk to shrimp and other inverts than the fish, but who knows? @Essjay is our resident chemist, and recommended Seachem's Cuprisorb to me. Claims to absorb copper and other heavy metals, so now I run it in the filter for a while when I set up a new tank. I'd also run some charcoal at the same time, help remove any traces of the meds or potentially any other chemical pollutants going on in there. Doesn't hurt (except in the wallet area, I'm sorry!) but might help?

2. The plants.
Where did you source your plants from? Can pm me the company, perhaps? I know that there's a large supplier in Lincolnshire that is featured a lot on Amazon, and that most of their aquatic plants for indoor tanks are imported and sprayed...

My contaminant that almost killed off my shrimp colony and required an emergency new set up was picking up four plants at my LFS. Over the next weeks, my shrimp began dying off, fish were fine though. I learned through @Essjay and other research online that all aquarium plants that are grown abroad and imported into the UK are required to be treated with certain pesticides, so they don't accidentally import invasive species into the UK. They spray or dip these plants into some nasty stuff, which isn't easy to remove, only breaks down very slowly over weeks and months, and wiped out most of my previously thriving shrimp colony. If you got a bad batch of plants from somewhere, there's a chance they were sprayed too much, left in the dip too long, the seller used some dodgy chemicals... some human error along the supply chain, you know? I only buy plants from Tropica or Pro-Shrimp now, or other hobbyists I trust, since they're in the EU and I know the plants won't have been treated with pesticides.

Even if it is the plants, my "toxic tank" did settle down after some months, the chemicals involved do gradually break down in water and in soil, so after some time, the tank became okay for shrimp again. Can link you some articles about this issue if you like.
So it wouldn't necessarily mean tearing them all out and starting over, especially if you run a lot of charcoal and the Cuprisorb, and potentially use the CO2 to grow the plant out faster/take cuttings/remove the older stuff and replant with new growth.

3. The wood/stone/substrate
I haven't googled the substrate, sorry, but if it's a proper planted tank substrate and has had more than a week to leach ammonia, and you're not getting ammonia readings, unlikely to be the source of the deaths.

The stone -can you get some photos of it? It looks like legit aquascaping rocks, but I'm a chemistry dunce, and I know @Essjay knows ways to test whether they could be contributing to fluctuating calcium levels or anything.

The wood- I don't like the dotting on the wood pieces you showed. The species of wood should be fine, but the dotting isn't usual biofilm (and yes, the brown stuff looks like normal diatom algae to me) and like @Naughts said, there can be harmless fungi or too much sap in the wood, or there could be something nasty. Since there's a mystery cause of deaths and it does seem like potentially poisoning/contamination, as a last resort I might remove the wood pieces... which is a shame, it's a lovely scape, and such a hassle if they're glued too, but if you rule out everything else and would tear the tank down anyway, might as well give it a go without those wood pieces, ya know?

Last thought that I'm sure you've already eliminated, but worth going through the checklist of possible problems - and thank you to anyone who bothered to read this far! But check with family and anyone else who is in the house often, that they're not using an airesols like air freshener, cleaning products, perfumes, essential oils etc in the same room as the tank? A non-fish keeper might not be so aware of the risks, and there have been cases of a partner using Windex to polish the glass, or using a fish only bucket to do some cleaning and contaminating the tank that way. Worth double checking and seeing if a contaminant is getting in that way.

Oh! Last last thought, not about the poisoning, but about the food - you've invested a lot of money and thought into the tank, equipment and testing etc, but don't skimp on the food...! Your basic King British type general flakes aren't great, and keeping pygmy cories myself, I picked @Byron 's brain about the best foods for cories, since they need a lot of small insects to be the main part of their diet. One of the best staple dry foods we can get in the UK is Bug Bites, and I crush their microgranules even smaller so it's great for pygmy cories and their fry. Instead of the frozen bloodworms, which aren't that nutritious, try to get small frozen insects like daphnia, cyclops, mosquito larvae, moina, baby brine shrimp - the dwarf cories, bronzes and endlers will go wild for any of those foods, trust me! Build them up a bit with some quality foods, can help boost their immune system and give them a better chance of battling off any illness.


Just my two cents worth, take anything you find useful and leave anything you don't! I'm crossing fingers for you and the fish!

 

[TwoTankAmin]

In the UK you guys should be able to get Ebo-Aquaristik from Germany. I feed their Softgran insect and the mussel to my corys and plecos. I have their shrip pellets and Veggie stick as well. It cost me to import it, but my fish never leave any uneaten when I feed it.

What I find difficult about the dying here is the time involved from when the fish go in to when they are dead. Usually contaminants work pretty fast and everything dies. But given all the water changes here there should be dilution and that should either slow or eliminate the deaths.

Normally I would consider the fish were arriving with something already if they did not do so well in the first smaller tank. And that still leaves me asking about the parameters in the small tank v.s. those in the bigger one.

A lot of figuring out what is wrong or in identifying potential disease or parasitic cause is a process of elimination. The more things we can rule out, the fewer should remain. But this doesn't always work. Another part of this is knowing one's fish. If one spends time watching their fish, you begin to notice how the normally behave. Ad you become more familiar with them, it becomes easier to notice when something is amiss. And this usually means there is some time for us to try and figure out what is going on.

A perfect example of this is noticing how a fish poops. Long stringy white poop is a clue. Or a fish not eating when the feeding frenzy begins is a clue.

As for adding CO2 to a planted tank, it complicates things. Light gets adjusted and so does fertilization. It is way more work to keep a high tech planted tank in good shape than a lower light tank with easier plants. There is a learning curve to planted tanks and it is usually not the best idea to start with adding CO2- either pressurized or DIY in ones earlier tanks.

I still would like to know the problem is not columnaris, but that means getting a good look at the fish, especially the mouth and then the rest of the body.

 

[AdoraBelle Dearheart]

In the UK you guys should be able to get Ebo-Aquaristik from Germany. I feed their Softgran insect and the mussel to my corys and plecos. I have their shrip pellets and Veggie stick as well. It cost me to import it, but my fish never leave any uneaten when I feed it.

Ooohh, I haven't heard of that one, thank you for the tip! I've been using some repashy recently since I'd heard good things and I like that I can coat the top of a pleco cave with the gel for them to lie and nom on it - the soylent green one is popular with the otos too!

What I find difficult about the dying here is the time involved from when the fish go in to when they are dead. Usually contaminants work pretty fast and everything dies. But given all the water changes here there should be dilution and that should either slow or eliminate the deaths.

That's what makes me wonder about a contaminant that builds up perhaps, or isn't easily water changed out, like a heavy metal, or like my friend who was losing fish slowly during covid because her toddler was putting his hands into the tank for the fish to nibble on when they returned from shopping and she was occupied bringing shopping in and things, while he still had hand sanitiser on his hands.

Only trace amounts, but something in at least one (and every shop was making us use different ones if we weren't carrying our own, and it was hard to buy for a while!) was toxic enough to cause sluggishness, suspicious bubbles on the surface, and on the 2nd or 3rd time it happened (before she figured out the cause) there was enough contamination to cause blindness and spinning due to bleeding on the brain; visible on her albino and light coloured cories and fatal to a good chunk of her stocking despite massive emergency water changes and moving fish to an emergency QT set up.
Several of us researched different hand sanitiser ingredients because some people didn't believe that could be the cause, but we did find at least one that had warnings about toxicity to aquatic life.
Dedicated and talented hobbyist, innocent kid, devastating results. Broke her heart, and mine broke for her.


Oh! And the combi-boiler! That reminds me - @mad_tunes , do you have a water softener or anything in your kitchen? Or could there be a problem with a storage tank, @Essjay ? Sorry to tag you a dozen times, Essjay! It's your own fault for being good with things like this

Normally I would consider the fish were arriving with something already if they did not do so well in the first smaller tank. And that still leaves me asking about the parameters in the small tank v.s. those in the bigger one.

A lot of figuring out what is wrong or in identifying potential disease or parasitic cause is a process of elimination. The more things we can rule out, the fewer should remain. But this doesn't always work. Another part of this is knowing one's fish. If one spends time watching their fish, you begin to notice how the normally behave. Ad you become more familiar with them, it becomes easier to notice when something is amiss. And this usually means there is some time for us to try and figure out what is going on.

A perfect example of this is noticing how a fish poops. Long stringy white poop is a clue. Or a fish not eating when the feeding frenzy begins is a clue.

Definitely to all of this!

I still would like to know the problem is not columnaris, but that means getting a good look at the fish, especially the mouth and then the rest of the body.

I wonder whether @mad_tunes could try shooting some video of the remaining fish, if any are still in there? I know photos are hard to get with small, fast and shy pygmies, but if you feed and lurk, video is usually easier, and more likely to spot something like columnaris than in still shots? If you do take any video of any of the tanks @mad_tunes , just be aware that the video upload function on this forum doesn't work. But if you upload to youtube or imgur or somewhere, can link it here for people to check out!

 

[mad_tunes]

1. For the tank itself:
I buy my tanks second hand as well, and have heard a few horror stories about things like copper and other heavy metals from a previous owner medicating the tank or something, remaining attached to the glass and silicone. Usually more of a risk to shrimp and other inverts than the fish, but who knows? @Essjay is our resident chemist, and recommended Seachem's Cuprisorb to me. Claims to absorb copper and other heavy metals, so now I run it in the filter for a while when I set up a new tank. I'd also run some charcoal at the same time, help remove any traces of the meds or potentially any other chemical pollutants going on in there. Doesn't hurt (except in the wallet area, I'm sorry!) but might help?

I have got some Zeo-carb, that I hadn't thought to use. I'll put it in the filter over the weekend.

Where did you source your plants from? Can pm me the company, perhaps? I know that there's a large supplier in Lincolnshire that is featured a lot on Amazon, and that most of their aquatic plants for indoor tanks are imported and sprayed...

£300 worth of plants came from Aquairum Gardens in Huntingdon. Understand why you mentioned PMing, but I've got no real reason to think they're the problem. Their advice seemed great. I spent way too long in their shop fannying about with rocks and wood with only encouragement. They're the only place I've ever seen with mock tanks that are a few inches high, so you can play with a layout of their wood and their rocks in the shop before buying anything-a great idea. If it might tally with anyone elses bad experiences after buying though, it should be public.

The stone -can you get some photos of it?

Here's some of the same batch that I ended up not using.
The bits that went in the tank had a scrub under hot water first.

But check with family and anyone else who is in the house often

Just me in the house. I do vape while in the front room with the two of the tanks, but not right next to them and it's not like I hotbox-it.

h! Last last thought, not about the poisoning, but about the food

Food... I've accrued more variety than I'd realised.

They get a mixture of these, with the 'Aquarium Complete Nutrition' flakes being the most regular and some frozen cubes of bloodworm every now and then too.

A perfect example of this is noticing how a fish poops

I've honestly never seen anything in the tank poop. Whenever I do see them, there's enough cover that things aren't out in the open for all that long.

do you have a water softener or anything in your kitchen

I don't. It's not new/recent pipework, copper pipe from when the place was built I'd guess. Combi-boilder that's a handful of years old.

I wonder whether @mad_tunes could try shooting some video of the remaining fish

Really hope you can all see these. Sorry about the quality. Tried to get in as close as I could and follow quick little fish, hope they don't make anyone motion-sick!

https://www.youtube.com/playlist?list=PLJsV-3VGX4PbxcjdLLaOm8_mTgch_sSZy

Can post individual links if it'd be better, but thought one might be preferred.

Spent a while watching the tank as I got the videos. There's a few more still swimming than I thought. They are all pretty shy though, not like I've seen tham at their most happy at all.
I might have seen some flashing against plants, jerky movements and maybe some slight white lips. I dunno though, maybe I'm just paranoid
On the up-side, I had 3 armoured shrimp in there at one point, which I hadn't seen for ages. I assumed the meds had taken them all out. I've got at least one left though! He was hanging out next to a malted shell, so maybe a recent malt was why he'd been hiding.
Heard a sparkling gourami making their croacking noises too, it's been a while since I'd heard them doing that.
(For anyone who hasn't had them - they really are fish that make noises. It's a thing, I swear!)

Really have to thank you all for your attention and effort. The thought, time and typing put into your posts has been awesome. Thank you all
If I've missed answering any questions, please do nudge me and I will. I haven't meant to ignore any.

 

[Byron]

I watched all the videos, thanks. A couple things to note. First, I do not see much if any of a fish problem such as disease. The pygmy gourami and the pygmy cories are basically behaving normally, with only a couple of possibly questionable fish.

I would definitely get some floating plants, and substantial ones like Water Sprite, Water Lettuce, Frogbit. Or some stem plants like Pennywort left floating. Both of these fish are used to cover, not direct overhead light, and they will be more calm which means less on edge or stressed.

There is what looks like some whitish fungus/slime on some of the wood. If it is, it could be toxic. The only way to know is examination by a microbiologist. Are fish dying? I had this toxic fungus once and it was very obvious. First was rapid respiration, but I don't see this here, followed by dyig fish until it was removed. Water also clouded some. That in't apparent here either, so the fungus, if that is what it is, may not be a problem.

The substrate is an issue though. First, it is not suitable for cories that expect to sift the sand through their gills. Second, it is 'aquagrowth soil' by Prodibio which is likely going to be a bacterial issues though usually with substrate fish, but the cories might succumb at some point.

 

[mad_tunes]

I watched all the videos, thanks. A couple things to note. First, I do not see much if any of a fish problem such as disease. The pygmy gourami and the pygmy cories are basically behaving normally, with only a couple of possibly questionable fish.

I would definitely get some floating plants, and substantial ones like Water Sprite, Water Lettuce, Frogbit. Or some stem plants like Pennywort left floating. Both of these fish are used to cover, not direct overhead light, and they will be more calm which means less on edge or stressed.

There is what looks like some whitish fungus/slime on some of the wood. If it is, it could be toxic. The only way to know is examination by a microbiologist. Are fish dying? I had this toxic fungus once and it was very obvious. First was rapid respiration, but I don't see this here, followed by dyig fish until it was removed. Water also clouded some. That in't apparent here either, so the fungus, if that is what it is, may not be a problem.

The substrate is an issue though. First, it is not suitable for cories that expect to sift the sand through their gills. Second, it is 'aquagrowth soil' by Prodibio which is likely going to be a bacterial issues though usually with substrate fish, but the cories might succumb at some point.

Thanks.
I was thinking it might all end up covered in plants so wouldn't be an issue. Is it just never a good idea to have Cory's with plants over the whole substrate?
They're really tiny, I guess the pygmy corys might need a *very* fine sand?
I'd like to understand how the substrate=bacteria issue if pos. How come pls?

Everything's more adventurous, out an about all the time, for the first week or so. Then they just retreat and I start to find bodys.
Is the retreating just settling into their hiding places, rather than a bad sign?

I'm settling into the idea of pulling it apart, cleaning as much as possible, then having a 2nd go with a different substrate.
There's a bit of a wasted gap behind the large bit of wood in the left corner, and under the wood on the right side, that annoy me anyway. Changing those wouldn't be a bad thing.
I've got a week off work at the end of April, so could spend a good amount of time on it again.

What substrate would tick all the boxes best?
Suitable for pygmy cories, kuhli loaches & shrimp
Easy to plant in
Feed plants long-term
As easy to maintain as possible
Dark coloured

I've got a dark sand in my two smaller tanks, and do really like it. It's pretty much intert as far as feeding plants goes though.
Does this all mean dirt with a sand cap? It's something I've not done before
What's the consensus on things like DIY osmocote 'root tabs'?

 

[TwoTankAmin]

I did notice a whitish lip and some white at the base of a dorsal. But I do not know if that is normal or not for the fish. Also, sometimes light can play tricks. I can not say with any certainty that there is columnaris involved. When mouth fungus progresses it can prevent a fish from eating. So make sure when you feed you watch the fish for a bit and try to make sure everyone eats.

It also appeared to me that some of the fish were grazing on the wood. I assume there is some biofilm there they want to nibble.

I think toxic slime on wood is a rare thing. Many of us got a bit of a coating on wood early on and it goes away. I also had mine munched on by a red tail black shark which sped that process.

Shrimp are usually much more sensitive to things than fish and that shrimp looked like it was doing just fine.

The plants look healthy as well, which is also a good sign.

As for vaping- when I started out with thanks I was a heavy smoker. I started to see a film on the surface of tanks and, fearing it was from my cigarettes, I got an Ionic Breeze air cleaner and it captured the smoke. What a mess to clean though. However, I never saw fish dying before I got the device and once I did , it cleaned the air pretty well. I never saw the film after that.

The good news is I managed to quit smoking tobacco about 14 years ago.

I am starting to drift back to wondering how heathy were the fish you got when you got them. Some stores are not so great re selling healthy fish.

 

[Byron]

They're really tiny, I guess the pygmy corys might need a *very* fine sand?

I'd like to understand how the substrate=bacteria issue if pos. How come pls?

Soft sand is essential for all species of Corydoras, They "expect" this because they filter feed the sand by taking up a mouthful, extracting any food bits, and expelling the sand through the gills. Second issue, bacteria. Gravel of the size in your tank dos not provide as good a bed for waste bacteria, the bacteria that decompose organic matter. This organic matter and excess food gets down in the gravel and "bad" bacteria result. With sand, this cannot occur. So sand is always a better substrate for such fish. I can't really explain this better, but it comes from Ian Fuller so I trust it.

If you do change the substrate, that is probably the best thing here. You are in the UK so look for Argos Play Sand; other UK members have used it and give it good reports. It is inexpensive, natural, and as safe as substrates can be for any fish or plants. As for plant nourishment, this comes from the breakdown of organics in the sand, one reason why so many of us with sand never touch it with the water changer or whatever. It is after all completely natural. Every species of Corydoras lives over either sand or silt with dried leaves sometimes. None live over gravel. There ar a few species that live over a mix of gravel and sand, but when one examines such areas it is obvious the sand is paramount.

It is easy to use substrate tabs for substrate-rooted plants that may benefit from this. And liquid supplements for all the plants. Aquatic plants assimilate some nutrients via the roots and other nutrients via their leaves.

Do not fuss with dirt, this is adding yet another bacteria issue that can harm fish.

 

[mad_tunes]

I've got Cory's and gouramis from two different places, once from shop 1 and then twice from shop 2. They're close to each other so may well have the same supplier themselves.
They did both drop their price at the same time. I'd guess they've all originated from the same place.

I was thinking the fish from shop 2 could have been the issue. Then I put the 2nd lot from shop 2 in one of my smaller tanks and they did fine for a few weeks.
Out in the open and swimming around as a nice little team just as you'd hope to see them.
Moved them to the larger one and had the same problems again after a week or so. They all seem to disappear and then some dead ones

I'll check out sand from argos All makes sense re sand and corys.
Good to know for tank v2

Re feeding, they're eager and pounce on food to begin with. Actively grabbing everything they can.. then they don't.
I fed them before taking those videos and they hardly seemed to notice or pay it any attention.
If I feed them during an evening it'll be gone by he next morning though

 

[Essjay]

I have got some Zeo-carb, that I hadn't thought to use. I'll put it in the filter over the weekend.

Please don't do this. Carbon is not needed routinely in a tank as it's main use is to remove medication after fish have been treated. Zeolite removes ammonia and starves the bacteria and plants. Cuprisorb, as used by Adorabelle, is totally different as it is designed to remove copper.

 

[kiko]

those tiny white flecks as you call them are caused by using an inline co2 diffuser...
also when using co2...some people will tell you 1 bubble per second...or 2 or whatever...
1bps using an inline diffuser would be the same as using like 5-10bps on a regular stick on glass with a V trap stone diffuser
in my experience with co2..things change with lights on/off and can cause too much variation throughout a single day and this swinging alone can kill fish
my advice when dealing with co2...get a co2 controller or simply don't use it...you can aim for a specific ph with an RO unit and root tabs for plants
when using a co2 controller regardless of lights on or off...it'll only turn on if it goes over/under what you set it at
also since you have a tds monitor...you should do water changes based on tds and not weekly...
so your tap comes out at 329 and from the 12 to the 18th it went up by 11points from 339 to 350 with half a ph point difference from tap
I would be doing water changes at 350...premix water for 7.1ph with an RO unit...or get an actual ph controller...
or get rid of the inline diffuser if you're going to keep using a bubble counter as a measuring device
I've actually posted about this before on how I do my water changes based on tds 50points off my tap
inline diffusers are way more effective than the traditional stick on glass stone diffusers but can also cause other issues like very fine bubbles sticking everywhere
I have one sitting in a drawer simply because of the white stuff on leafs/wood or the water looking "foggy"
simply get a ph pen...and measure the ph 4 times a day...and check how much it swings...anything over half a ph point in a single day..to me is a fish killer..
it might be fine for a few days...but not on an ongoing basis...

 

[mad_tunes]

those tiny white flecks as you call them are caused by using an inline co2 diffuser...
also when using co2...some people will tell you 1 bubble per second...or 2 or whatever...
1bps using an inline diffuser would be the same as using like 5-10bps on a regular stick on glass with a V trap stone diffuser
in my experience with co2..things change with lights on/off and can cause too much variation throughout a single day and this swinging alone can kill fish
my advice when dealing with co2...get a co2 controller or simply don't use it...you can aim for a specific ph with an RO unit and root tabs for plants
when using a co2 controller regardless of lights on or off...it'll only turn on if it goes over/under what you set it at
also since you have a tds monitor...you should do water changes based on tds and not weekly...
so your tap comes out at 329 and from the 12 to the 18th it went up by 11points from 339 to 350 with half a ph point difference from tap
I would be doing water changes at 350...premix water for 7.1ph with an RO unit...or get an actual ph controller...
or get rid of the inline diffuser if you're going to keep using a bubble counter as a measuring device
I've actually posted about this before on how I do my water changes based on tds 50points off my tap
inline diffusers are way more effective than the traditional stick on glass stone diffusers but can also cause other issues like very fine bubbles sticking everywhere
I have one sitting in a drawer simply because of the white stuff on leafs/wood or the water looking "foggy"
simply get a ph pen...and measure the ph 4 times a day...and check how much it swings...anything over half a ph point in a single day..to me is a fish killer..
it might be fine for a few days...but not on an ongoing basis...

Really good to know thanks. I was thinking it was the sign if some parasite 'not on the fish' stage at one point

Ive got a pH pen, cheap one very like the TDS one I've got.
Once things are levelled out a bit and I get back on the CO2, I was going to monitor throughout a day or three just as you describe

 

[TwoTankAmin]

I have to say that I ran pressurized CO@ on a tank for almost a decade, I had no space for fanncy equipment nor the budget for a pH controller etc. My system was dirt simple. I ran the output of my CO2 line directly into the intake of the Eheim Pro II 2026 filter/ I would not use any other brand as I feared they would not stand up to having gas bubbles inside it.

For the first few weeks I was contantly testing. I was prepared to add an airstone on a timer to outgas CO2 overnight so my system could run 24/7 and be safe. In the end I discovered running 1 bps worked great. The overnight build-up wasn't an issue. Anyhting I planted thrived as did the fish. In the end I repurposed the tank and sold the CO2 system. The reason was the growth was so lush that I spent more time caring for the plants in this tank than I did working on any other tank even those much bigger.

That said, there is a ton of very pricey equipment and supplies that one can buy for a planted tank. My personal feeling is most of them are not needed, cost way too much and do not make much of a difference. I used small aquarium gravel and a bit of laterite as the substrate and relied mostly on mulm to keep plant healthy. I use Jobes Spikes to fertilize the substrate and Tropica liquid ferts in the water.

The one thing I did was to but a high quality needle valve for adjusting the bubble rate in the tank.

Bear in mind that in nature parameter change over the 24 hours of each day. Moreover, they also change seasonally. This is perfectly natural. If such changes were harmful to fish and aquatic plants, nature would not work, but it does.

edited to fix typos