I set up a 40g black water tank and added 25 Khuli loaches. I’ve had them in there for about three weeks and 10 of the loaches have died, and I have no idea why. The parameters are exactly where they should be, I feed them, I see them playing, then one turns up dead. I also have 14 espei rasboras in the same tank, and they’re fine. This is my first time keeping these fish. Is there something special I need to know? I thought I did enough research before buying them, but maybe I missed something.