Or something else? Fish dropping like flies, only a couple of guppies git a couple of white spots. My plattys that have died had nothing visable, just got listless and then died. Lost several fish in last 48 hours.
Did a 30% water change Friday, a 50% yesterday and changed sand for gravel (gravel soaked and rinsed but fish were dying before then anyway)
Ph is 7.5
Ammonia 0
NitrIte 0
Nitrate 20-40
Community tank, understocked, 30%
pwc done weekly, fish fed every other day alternate flakes, bloodworms, fresh veg and algae wafers for bn plec.

Any help appreciated.