Are you running CO2? I had horrible cardinal loses with CO2. I learned that I had to turn off the CO2 the day before introducing cardinals to let the tank outgas, then turn it back on a day later after adding the cardinals.
No losses after doing that.
Hmmm. I do have a CO2 diffuser but I don't think it really works anyway cus it is stuck behind the foxtail. I do dose with excell so that might be the problem. Thanks for that idea.