Hi team, I'm still at work and my partner and kids just contacted me after school. We put 9 cardinal tetra into our cycled 21L QT 3 days ago. I tested their ammonia & nitrite daily...until this morning (of course). My family found 4 dead cardinals with 2 others who didn't look happy. They removed the dead ones, rang me, and i talked them through putting in the right amount of prime and stability. Then i talked them through how to do the parameter tests. temp 26*C ammonia .2 - .25 max nitrite 0ppm nitrate "looks like 5ppm but at worst could be 10ppm" is what my 11 yo said. she said "there's no red at all, just orange." But 4 dead fish at the same time on the same day tells me it's very likely to either be: * water quality/temp * food? no signs of other illness except a few looked a bit "chubby" to me since we got them. this morning i fed them a tiny bit of good quality flakes and a few broken off pieces of the JBL Novotab stick-on-the tank fish food (they haven't figured out how to eat it off the tank, so i broke off maybe 1/5 of a tab to add to the tank to feed them). it *could* be that there was a slight ammonia spike that killed the first one and then that killed the others? i dosed with prime the day before yesterday but maybe? or, something else killed them and the ammonia is because of the dead fish in the tank all day? tbh, i noticed at least 6 or 7 swimming this morning for feeding but i didn't try to count all 9 so one could have been dead overnight. my family said there was only 1 that looked pale and like it had been dead for half a day or more, the others looked like they had just died and my family wasn't convinced they were dead at first...until they didn't move with the net and well, you know the look. i always rinse my hands very well in rainwater before putting them in the tank to do anything, including feeding. but, this IS the same QT where we've had mysterious unexplained sterbai deaths. other theory is that having 9 tiny cardinals in a 21L QT stressed them out? it was only for their QT period, and their DT is 165L... i'm heading home shortly...any ideas? @AJBrown ... i'm so distressed!