Lost two bandit cories. Could dosing plant fert be the cause?

Hi - first post

Lost two bandit cories in 3 weeks. I would love a reason and some advice.

I have a 15 gallon tank in my classroom. It is heavily planted. I add 2ml of easycarbo, 1ml Flourish phosphorous, 1ml TNC lite daily Mon to Friday. Monday I dose 4ml of API leaf zone.
My water parameters are below:
Ammonia 0ppm
Nitrite 0ppm
Nitrate 10-20ppm
Phosphate 1-2ppm
gH 8
kH 4
Temp 24C
Substrate is sand. Water change is 20% weekly. I use RO water which I add hardness as the water where I live is very hard and 40ppm nitrates. For light I have 2x NICREW Super Bright LED 11Ws on a 8 hour cycle.
Fauna - 5x Harlequin Rasbora, 1xHoney Gourami, 4xBandit Cory(was 6), 1x Bristlenose pleco (juvenile), 5 nertite snails, 3 amano shrimp
The tank has been running for a year and a half and has been very stable for at least a year with little variation from the above parameters.
Before that I made every mistake you could possible make while managing to keep all the above fish (bar the pleco). The only exception is another honey gourami that died due to the 32C heat in my classroom so I now take the tank home when the summer heat starts. No dosing or feeding over the weekend. Holidays I pop in a couple of times a week and use an automatic feeder. I feed the cories on catfish sinking pellets and the occasional brineshimp/bloodworm treat.

Only things that have changed in the near past are:
1) The addition of the pleco who will be moving to the home tank I'm planning in July.
2) Dosing with API leaf zone
3) Appearance of blue-green algae on my floating plants - the plants were growing like crazy but have started suffering the last few weeks. Before I was throwing away handfuls weekly.

I love the cories but admit that getting them for a classroom tank was a mistake as they spend the whole day hiding and I'm the only one that enjoys them. I also feel the tank is to small for them and needs more open space for them to feed so I am planning to move them to a home tank when I've moved house.

I'm baffled as to why there dying as they survived everything my inexperience has thrown at them in the first 6 months. Overfeeding from students, nitrates in the 60ppm, water temps of 28Cs and my disastrous attempt at mixing in soil substrate to the sand which turned the tank cloudy for 10 days.

I have a photo of the one of the dead cories, the tank and some of the algae. If someone can tell me how to share them I will

Help! (and thanks in advance)

First quickly on the photos...at the bottom of a new post is as button "Upload a File," click that, then click the link of the photo on your PC. If it says it is too large, reduce the resolution. Beyond this, I can't offer anything.

To the issue. You are adding too many additives and while I certainly cannot say this killed the cories, I can say that the fish were seriously compromised/weakened by all these additives.

There is no reason to be adding Flourish Phosphorus; there is more than sufficient from fish foods. This is likely one issue with the cyanobacteria (blue green algae which is not an algae but a bacteria) which occurs from organics and light. Nitrate close to 20 ppm is a sign of organic issues, and the soil is likely another. Nitr4ates do detrimentally affect fish too, so that is another weakening factor.

The EasyCarbo is likely a real problem. I cannot find the ingredients (I also worry when a manufacturer won't say what is in a product) but from the claim that it kills algae I suspect it is glutaraldehyde. Seachem's Excel and API's CO2 Booster are both the same ingredient. This is very toxic and strong disinfectant used to sterilize surgical instruments in hospitals, in embalming fluid, in anti-freeze, in ship ballasts to kill bacteria...you get the idea. This should never be added to an aquarium with live fish. The fact that it will kill algae should bee a caution never to use it. This will affect the physiology of fish, and cories are especially sensitive to any chemical additive. This could also be the issue with plant degeneration as some plants will be killed even with recommended doses of these products (Vallisneria is especially sensitive, there are others).

API LeafZone is not that directly dangerous but it is not a good supplement as it is only iron and potassium, and that leaves out all the other 15 or so nutrients. Could also be a factor in the cyanobacteria, with too much iron. Iron is a heavy metal and very toxic to fish if more than what the plants can readily take up is being added, and I suspect it is here.

Another issue is the temperature...32C is much too warm for cories. Over time this too weakens the fish as the higher temperature drives their metabolism and they have to work much harder just to maintain normal physiological functions so in time they weaken and succumb to this and that, and they will not have anywhere near a normal lifespan of 15 years.

Hope this helps some.

Hi and welcome to the forum

Byron has covered most of it. Stop adding chemicals. If you want to add an aquarium plant fertiliser, use a liquid iron based fertiliser and get an iron test kit to monitor the levels in the water. You only need 1ppm of iron for the plants, any higher and the fish suffer from iron poisoning.

---------------------------
32C shouldn't be an issue for gouramis because they naturally occur in warm shallow water with a low oxygen level.

Corydoras can tolerate 30C for a short time (a few weeks) but higher temperatures or longer periods in warm water will stress or kill them.

If you have warm water during summer, increase aeration/ surface turbulence to maximise oxygen levels in the water.

---------------------------
Post pictures of the sick/ dead fish.

---------------------------
Do bigger water changes. Clean the filter at least once a month. Make sure cleaning staff aren't spraying anything on the tank.

You do water changes for 2 main reasons.
1) to reduce nutrients like ammonia, nitrite & nitrate.
2) to dilute disease organisms in the water.

Fish live in a soup of microscopic organisms including bacteria, fungus, viruses, protozoans, worms, flukes and various other things that make your skin crawl. Doing a big water change and gravel cleaning the substrate on a regular basis will dilute these organisms and reduce their numbers in the water, thus making it a safer and healthier environment for the fish.

If you do a 25% water change each week you leave behind 75% of the bad stuff in the water.
If you do a 50% water change each week you leave behind 50% of the bad stuff in the water.
If you do a 75% water change each week you leave behind 25% of the bad stuff in the water.

Fish live in their own waste. Their tank and filter is full of fish poop. The water they breath is filtered through fish poop. Cleaning filters, gravel and doing big regular water changes, removes a lot of this poop and makes the environment cleaner and healthier for the fish.

Cheers for the advice guys.

I've moved the tank home to avoid the summer temperatures in my classroom. I've also upped my water changes to 50% weekly and cleared out all signs of blue/green algae from the tank (not bleach or anything used)

I was dosing phosphate as I found I would get high nitrate and no phosphate. If I added the phosphate the floating plants would grow rapidly and keep the nitrates down. I don't think ammonia or nitrite is a problem as I regularly test for it and never get any. The tests do work as I tested the water of another teachers goldfish tank and got crazy levels of both.

Is 20ppm definitely to high for nitrate? My local fish shop told me it was fine.

I've stopped dosing and have bought an iron testing kit. Think its all working as my corys are far more active.

Attached the photos - still open to any other advice. As I said all the green-blue algae is gone. I binned all the floating plants to do this and put new ones in.

You want the nitrate level as low as possible. However, it's almost impossible to keep nitrates at 0 so we recommend keeping the nitrates below 20ppm.

--------------------------
Most true aquatic plants don't use phosphates and pretty much every country around the world is trying to limit the use of phosphates in detergents because they get into the environment and encourage true algae and blue green algae (Cyanobacteria).

--------------------------
The Corydoras in the picture appears to have a bacterial infection (big red patch on its belly). It can be caused by rotten food, poor water quality, introduced by other fish or plants, or the blue green algae contributed to it.

When blue green algae is growing on the bottom of the tank, any fish or shrimp or snail that lives on the bottom, will be more susceptible to poisoning form the blue green algae, which naturally produces toxins that irritate and kill things. Cories live on the bottom and if they are in direct contact with the blue green algae, there is a chance they will get sick and die because of it.

--------------------------
You need a picture on the back of the tank to make the fish feel more secure.

JonU said:

Is 20ppm definitely to high for nitrate? My local fish shop told me it was fine.

Click to expand...

As Colin said, keeping nitrates at zero (which without any question would be best for our fish) is usually unrealistic (heavily planted natural/low-tech tanks can often achieve this) but keeping it as low as possible and certainly below 20 ppm is very important. There is widespread opinion among professional ichthyologically-minded aquarists that many fish are more susceptible to nitrates than used to be assumed and over time nitrate is weakening them at the very least so they become more susceptible to other problems.

Most fish store employees are not trained ichthyologists/bioogists, and even worse few have the will to research before advising.