Me again!
I am SOOO stupid sometimes.
I was doing the water change in Yoshi's tank tonight (Small Hospital tank) and thought, "Why are there all these empty snail shells?"
The medication killed the snails! That means even though I was doing large water changes there were rotting snail corpses polluting the water the moment it went in there! DOH!
Tonight is the night Yoshi moves from Tank3 to his home Tank1 so while the tank is empty of fish i'll replace all the "gravel"
(I left him in the medicated tank for an extra 7 days to make sure he wasn't going to spread something to the rest of the population.)
Hope that makes sense to everyone
Bis