I found 4 dead corydoras in my tank, 2 julii and 2 panda.
Water parameters are perfect, only thing that I I could say is that ammonia is at 0.25 which I don't think is enough to kill my cories, they were all in the same corner.
Is a 55 gallon heated to 78 degrees, and sorority lives there but they have been getting along fine and I don't think, the bettas are responsible, only thing that's is different is that I switched to play sand but I cleaned it throughly before adding it and filters were already running for almost 6 months and I also left some old gravel inside a Styrofoam cup to help the growth of beneficial bacteria. I also added 3 black kuhli loaches yesterday but those were quarantined before adding to the tank and some malaysian trumpet snails quarantined as well.
Like I said, water is perfect, tank is clean and plenty of filtration, currently using an aquaclear 70 and a penguin 350. Could the kuhli loaches be responsible? Those are supposed to be peaceful, please help.