"Bill K" wrote in message
I had the unfortunate incident of a massive fish die-off in my tank
I'm after 4 things...
1) What happened?
The presence of nitrites (2ppm) either indicates an ammonia spike occured
earlier, or the nitrite oxidizing bacteria were inhibited (nitrobacter is
more strongly affected by loss dissolved oxygen than nitrosomonas). If
ammonia spike, this would be partly responsible for the stress on the
fish. Having the pump off (2 hours and them 5 hours) would indicate that
the O2 levels would have dropped during these periods. The 5 hours the
filter was off would be sufficient for the bacteria to go anaerobic. The
fish could have been exposed to the noxious water put into the tank from
the filter, after riding an ammonia spike, and during lower than normal
O2 levels (a 3 punch knockout with a moderately loaded tank?)
2) Did I do the correct measures, immediately and subsequently?
3) Where do I go from here?
4) Let others know, so the same mistakes are not made
I try to service canisters in under 30 minutes. Heavily populated tanks
really require multiple filters, or as a minimum, an airstone running. I
don't perscribe to the paint theory. I'm more inclined to consider
sulphide gas release during substrate agitation, but you discounted this
This is mostly speculation. You could easily have suffered from a pH
crash, and after so many water changes, your pH would have been normal,
or there was nothing you did which was significant enough, and an O2
difficiency (algae bloom?) or some chemicals (high chlorine levels) were
present and with massive water changes, responsible. Sorry for your
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