Nitrate Way Too High And Fish Dying

[This Old Spouse]

If your tank was set up for a long time and this is the first time in a while you've done such a thorough cleaning, you may have stirred something up that disagreed with the tetras. Hard to tell. I still don't think it was necessarily the nitrates, and I'd be loathe to use any kind of chemical to adjust it.

 

[fishy16]

Thats what im thinking. My tank is quite heavily planted and so i dont do that much in the way of water changes and cleaning, it pretty much looks after its self. Ive never had high readings before so this was a shock,(been set up 1 year now) they've always been 0 or well within safe figures. I didnt go with the nitra zorb in the end i'd rather go with more natural stuff and water changes if it occurs again. Many thanks to everyone who offered advise its a pity i couldnt get to the bottom of it though...