Corydoras dying but no disease evidence.

[FranJ]

My tank was has been setup for over 6 months. I did have 7 albino and 2 pepper and 6 sterba Corys with 5 white cloud, 7 Rasboras, 1 clown pleco and about 6 super red pleco babies. This is a 36 bow front. All live plants in bdb

I fed them this morning...not thinking and then did my water testing. 

Parameters: pH- 8.0-8.2, Ammonia- 0ppm, Nitrate- 80ppm, nitrite 0ppm....

This tank has been getting water changes about every 2 weeks 10 to 15 gallons. We did miss 1 recently. We had a death in the family and we're dealing with that.

The Corydoras that died were doing really well prior. I have since added a seasoned sponge filter in addition to the HOB. I also have a UV sterilizer in this tank.

[gardenman]

How many corydoras died? One is not an issue. Fish die. Often for completely unknown reasons. It happens. If you've lost several, then it's more of a concern. Internal parasites are often an issue with corys. They live on the bottom and most internal parasites get passed through feces and the corys are down where the feces are. It's easy for them to pick up an internal parasite where a top dwelling fish like a hatchet fish or butterfly fish might be less inclined to encounter the parasite. IF there are significant casualties, I'd suspect an internal parasite.

The paranoid part of me worries more about your tank being supported by two separate platforms. It's working for you, but it would scare me. Any difference in the height or stability of one of the two platforms could create stress on the structure of the tank which could lead to problems down the road.

[FranJ]

I had 5 total die. They were swimming around and doing great then bam... floating at the top. They were going up for air the night before....but they do that. I'm doing a 25% or 50% water change today. I'm hoping that will get this back under control. I also noticed several of my ramshorn snail shells are empty. Not sure what that is about.

Should I take them to quarantine and treat for parasite? I QT all my fish and plants with co-op trio. But I can get them all over to QT. Or should I treat the entire tank?

My husband is building a stand out of 2x4's we will have it up soon. Those tables are heavy pine. I understand what you mean about 2 tables. It is being fixed.

Thank you for responding!

Edited June 26, 2021 by FranJ
Missing some info

[eatyourpeas]

Your Nitrates are a little high. I wonder if you had an Ammonia spike due to snail deaths and that caused stress on the Corys. @gardenman has a good point regarding the bottom, and based on that I would also do a gravel vacuum when you do your WC.

[gardenman]

Five is a lot. I would worry about internal parasites being the cause with that many deaths. I'd probably treat the whole tank to be safe. With just the corys dying it would seem to be something they were coming into contact with more than the other fish.