My Guppy population is decimated, please help!

Hello

I have a 70 liters mature tank (had it running for over a year now), with several live plants in it.

It started with fish population of 3 female Guppy and 2 male Guppy Endlers, plus 2 biggish Black Devil Snails.

The Guppy reproduced a lot, so eventually it was a bit crowded, but a healthy population. Between adults and fry probably around 30 of them in total, but all very small, maybe 1,5 / 2 cm in length max.

I change roughly 25% of the tank water, every 3/4 weeks, using tap water with water conditioner.
I check a few water parameters quite often, today for example these are the results:

NH3/NH4 - 0
NO2 - 0
NO3 - around 40 mg/L (sometimes it is lower around 25-30)

Temperature 26C

Sorry about missing values, but those are the only water analysis kits I could afford!

Everything seemed fine for about a year until about 3 weeks ago, when I had the bad idea of purchasing 1 new male and 1 new female to add new genes to the pool, as I was concerned about the heavy inbreeding going on. On the same day I also purchased for the first time Daphnia gel food by Tetra, they are small sachets to give as a snack once a week, to integrate to the flakes that I normally feed them daily.

Within a couple days hell started!

First I started to notice that the fish were keeping their dorsal fin very low, almost attached onto the body, and the tails also looked somehow 'clumped'.

Just a couple of days later I could see that they were already wasting away, losing weight and looking very pale (almost all of them!!). The dorsal fin and tail had almost disappeared, the tails looked very 'pointy', making my poor Guppy look somehow 'bullet shaped', I attach here a couple of images of a female with the disease. Also the poo looked in some parts almost 'transparent'.

I have seen fish rot many years ago on a Betta that I used to have and it looked very different, for a starter it was very gradual while this disease is killing them super quick, I could see the tail being consumed by it slowly, this looks very different to me, sorry I can't explain it better.

Then the deaths started. Once the 'bullet' shape appeared within 24 hours they were on the bottom of the tank struggling, another 24 hours and they were dead.

I have lost roughly 10 fish (between adults and fry) within the first 3/4 days. So I went to the shop, and even though the shop assistant had no idea of what disease it could be, I was given a medicine called Rivamor. It should be useful for a number of diseases I was told.

So I added the medicine in the water and followed all the instructions: removed the filter with the good bacteria to save them, waited 4 days without feeding, then on day 5 did a 30% water change.

I was hoping the deaths would stop, but no, roughly 10 more fish died after that. I feel so sorry for them and so impotent, because I don't know what to do. In total so far I have lost around 20 fish (between adults and youngsters). My tank looks very empty now, I have only 3 adults left and a couple of fry, plus the 2 snails (luckily they seem fine!).

I am scared that the deaths are not over yet, despite the medicine treatment. I don't know what to do, please help!

I am not even sure if the disease was from the 2 new fish added or from the contaminated Daphnia gel food. I have not given the Daphnia gel food anymore, to avoid risking to make it worse.

Any advice?

I have so little experience with disease issues that I do not say much about such issues, but a couple things do stand out here.

Nitrate over 20ppm (ppm = mg/l) is not good for any fish. This is not likely to cause the deaths as you describe, but high nitrate does weaken fish making them more susceptible to other issues, so this should be looked into.

Partial water changes must be every week, not every 3 or 4 weeks. And a substantial volume should be changed at each, at least 50% but preferably 60-70% of the tank volume. Provided parameters (GH and pH and temperature) of tap water and tank water are relatively the same, this will benefit and cause no harm at all. I would do a couple of major water changes immediately; it is amazing how beneficial just this can be.

Third thing...what is the GH and pH of your source water and tank water? The tap water GH and pH you should be able to ascertain from your water authority, check their website. A pH test is a good tool to have as changes in pH in the tank can be telling.

I would recommend performing a thorough cleaning of the tank, including cleaning the gravel and any decorations, as soon as possible. Add 40% new water when putting the water back in. Observe the fish for 24 hours and if still no change you may want to add some salt.

Byron said:

I have so little experience with disease issues that I do not say much about such issues, but a couple things do stand out here.

Nitrate over 20ppm (ppm = mg/l) is not good for any fish. This is not likely to cause the deaths as you describe, but high nitrate does weaken fish making them more susceptible to other issues, so this should bee looked into.

Partial water changes must be every week, not every 3 or 4 weeks. And a substantial volume should be changed at each, at least 50% but preferably 60-70% of the tank volume. Provided parameters (GH and pH and temperature) of tap water and tank water are relatively the same, this will benefit and cause no harm at all. I would do a couple of major water changes immediately; it is amazing how beneficial just this can be.

Third thing...what is the GH and pH of your source water and tank water? The tap water GH and pH you should bee able to ascertain from your water authority, check their website. A pH test is a good tool to have as changes in pH in the tank can bee telling.

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Hello Byron and thank you for your precious advice!

I have just checked on my water authority website like you suggested (great tip!) and I figured out a little more, for example that in my specific area PH is 7,4 and GH 29,8 what do you think, is it ok for Guppy?

Another thing I also found out is that Nitrate in my tap water is 25 mg/L , so it's already too high according to your guidelines

I had previously believed that up to 50 mg/L was ok for fish (it could create algae but not harm the fish). According to what you said basically my tap water is already too high in Nitrate naturally, so I guess I will have to start buying water from the pet store, at least for part of my water changes, what do you think?

I didn't know water changes needed to be done weekly, however if I don't start using better water I guess it will not help in reducing Nitrate to optimal levels

I will do a couple of major water changes as you suggested for sure, trying to match the temperature to avoid shocking the fish, however I guess I should be extra careful now if I start mixing tap water with pet store water?

yeti79 said:

I would recommend performing a thorough cleaning of the tank, including cleaning the gravel and any decorations, as soon as possible. Add 40% new water when putting the water back in. Observe the fish for 24 hours and if still no change you may want to add some salt.

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Hello Yeti thank you for your advice, yes I am organizing a major water change will do it tonight.

However can you explain a bit better about the salt? I never used salt before, do you mean regular cooking salt or a different kind? How much of it? Would it harm the snails? I love my two snails would not want to harm them.

chiara said:

Hello Yeti thank you for your advice, yes I am organizing a major water change will do it tonight.

However can you explain a bit better about the salt? I never used salt before, do you mean regular cooking salt or a different kind? How much of it? Would it harm the snails? I love my two snails would not want to harm them.

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Not regular table salt because it has iodine added to it. You would want to get aquarium salt. It is widely used in the hobby as a medicine I would not recommend salt unless you take out the plants because it may kill them. Here is a useful article that should help you out https://www.aquariumcoop.com/blogs/aquarium/aquarium-salt-for-sick-fish
I do not know about snails, hopefully someone else here could help you with that information

A few issues have surfaced in the last couple of posts.

First, I would not use salt here as it is not likely going to help. Salt can be the best treatment for some issues, but it does impact fish negatively so its use has to be controlled, meaning only when it is without doubt the best treatment for the problem. I would be inclined to hold off on salt, unless someone sees an issue--as I said, my experience with specific diseases is next to nil (fortunately) but one thing I have learned is not to use additives/medications unless it is pretty certain what is needed.

The GH of 29.8, is this 29.8 ppm (= mg/l), or 29.8 dGH, or some other unit? This makes a big difference, so let us know the unit of measure the water authority uses. If this is 28 dGH, the water is very, very hard (fine for guppies), but if it is 28 ppm (mg/l) it is very soft, very, very bad for guppies. This could be the real issue here; I can detail this more once we have the unit sorted out.

The nitrates...using some form of "pure" water is one method, but will get very expensive in no time. There aree members here who have dealt with high nitrates in their source water and they can best detail how they deal with this problem. They may see this thread and comment, but one member I know who does this is @AbbeysDad and I believe @seangee has as well.

I have nitrates in my well water the result (I believe) from a 95 acre farmers field across the road that gets ample fertilizers. I pre-filter most water for water changes using a now discontinued API Tap Water Filter filled with API Nitra-Zorb. Nitra-zorb us sold in pouches meant to be placed in filters so you might use it this way to get tank nitrates down. The nitra-zorb can be recharged many times using ordinary non-iodized table or aquarium salt. The effectiveness and use life is reduced by detritus coating the resin pellets so it should be placed last is the filter after fine media.
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I believe @seangee has used a Pozanni filter to remove nitrates from his source water which amy or may not be available in the US (I did not check to see your location). There are also inline nitrate filters available, but these filters/cartridges may be cost prohibitive.
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Nitrates in your source water may not be as bad as nitrates in your tank water. I believe that nitrates at high levels are bad, but tank nitrates keep bad company as there are also other pollutants we don't/can't test for.
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Having 'said' all this, you need to step up your water changes, AND stay on top of filter maintenance and gravel vacuuming to get/keep tank nitrates as low as possible. And then there are fast growing floating plants that help as well.
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It's unclear if you have or had "old tank syndrome" (although it seems likely*) or whether the new fish you added brought some parasite or disease. If the increased water changes and tank maintenance don't resolve the problems, you could try API General Cure (I don't like meds much) OR you may face a tear down and restart (last resort).
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* I'm thinking old tank syndrome because of your 3-4 week water change and your growing population (uncertain about filter and gravel cleaning). Pollution (nitrates) slowly increases and water becomes acidic as pH lowers. At some point, the tank crashes as most inhabitants succumb to the poor water quality.
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My apologies for going on and on. I hope your trouble resolves!

Ok lets think this through logically (bear with me there is a lot).
I can't provide a diagnosis based on the info provided but the most likely causes are a pathogen or disease that came in with either the new fish or the food. My money is on the fish.

Nitrates at the levels you mention did not wipe out your tank. As @Byron suggests it will reduce the life of your fish but won't wipe them out in one hit. Similarly the hardness (or softness) did not kill them. You need to establish what this is but your guppies would not have survived a year, or had fry, if it was 29ppm.

But there may be a new problem. Bacterial medication probably killed the good bacteria in your tank. Removing the filter would only have preserved the bacteria if the media remained wet and was in flowing water most of the time. SO it is actually possible that you now have a completely uncycled tank. SInce you have the ammonia and nitrite tests test these every day and do a 75% water change any time you get any value other than 0. I would do 75% daily changes for a few days regardless of the results. Don't bother testing for anything else now. We do need to address the nitrates and establish what the hardness is and if there is anything that should be done - but these are for another day. Changing those now is not going to make any difference. Personally I would not add any more treatments. Either they will recover or they won't (sorry).

Lets just focus on the immediate problem of keeping them alive and getting them back to health. Once that is done we can re-visit any future actions.

Edit: My post crossed with @AbbeysDad - while we can't rule out old tank syndrome there is still a good chance that the problem has effectively become new tank syndrome.

Yes, you may be right @seangee - the lack of weekly water changes and increasing stock levels along with questionable maintenance may have led to old tank syndrome. This lowered immunities and increased the potential for bacterial infection. The rivamor may be a good anti-bacteria, but may very well have decimated the beneficial bacteria...leading to a spike in ammonia.

Hello everyone, thank you so much for your help!

I have done 2 major water changes over the weekend, with careful gravel vacuuming. I have only had one more dead fish on Friday, after that no more yay!! and as of today the few survivors are looking much much better I have to say, so much so that I am hopeful they will be ok

Latest news: some just born fry appeared today, I guess they must be 24 hours old or so

I have not given salt, nor other medicines, just water changes like you guys suggested and I think they did the trick...

@Byron in regards to the GH: I went back to the website to check the unit and they do not actually specify if it is mg/L , so I am assuming is 29,8 DGH, as I have noticed it being very hard (leaves sometimes white marks on glasses), so it should be ok for guppy I guess?
As you suggested I will do more frequent and more heavy water changes from now on so I can hopefully keep nitrates at bay without having to switch to expensive store bought water...

@AbbeysDad thank you for your advice! I will check out Nitra-zorb for sure (if I can find it here in Italy where I live!) or a similar solution, sounds like what I need. I will also buy more plants, (great tip thank you), to help with nitrate and make the aquarium even more beautiful

In regards to old tank syndrome: yes, it could have been, however it would be too much of a coincidence that the deaths started right after introducing the 2 new fish and (perhaps) contaminated food, so to me it seems very likely that it was a bad bacterial/parasite infection... however it could have been.

@seangee thank you so much for your advice! yes as you said the nitrate issue (which I will have to resolve) didn't cause the massive sudden deaths, and yes I am pretty sure it's 29 GDH and not ppm. I am well aware of how bad medication are, I call them 'the nuke' but I decided to go ahead and use it because I was desperate to save at least a few fish. When I removed the filter I placed it in a container with aquarium water (not flowing unfortunately), but I guess they must have survived at least in part, otherwise I now would not have value of 0 NH3/NH4 and 0
NO2 isn't it?

chiara said:

@Byron in regards to the GH: I went back to the website to check the unit and they do not actually specify if it is mg/L , so I am assuming is 29,8 DGH, as I have noticed it being very hard (leaves sometimes white marks on glasses), so it should be ok for guppy I guess?
As you suggested I will do more frequent and more heavy water changes from now on so I can hopefully keep nitrates at bay without having to switch to expensive store bought water...

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Yes to all of this. Guppies will be find if the assumption of 29 dGH or anywhere remotely close to that high a number is correct. And increase the water changes, yes.