Nitrite spike in cycled tank
I know nitrites and the nitrogen cycle are covered in depth on this forum and I know how it all works. My tank is 3 months old and has been cycled for 2 of those months. I did a 50% water change yesterday and I was pretty careful to let the dechlor (sodium thiosulfate) to let mix in before pouring water from buckets into the tank. The water here does not contain chloramines only chlorine. I left for the day and came back and there were several dead fish and a number of dead RCS. All of the inhabitants including the snails were trying desperately to be at the top mm of water. I immediately tested nitrites and ammonia. Ammonia was a slight shade darker than 0ppm but there were dead animals in the tank so thats not too suprising. The nitrites were over .5ppm, I did another 50% water change and retested nitrites to make sure they went down and they did by 50%. I woke up and retested nitrites again this morning and they were slightly less than .5 ppm. I again did another water change to lower them and left the water level a little lower to make sure there was a good oxygen mixture from the surface to the animals had a little easier time breathing.
This has happened once before (very early on in the cycling) when I did a large water change, but that time i know it had a mini cycle but the ammonia and nitrites were gone within 24 hrs. I have an established biofilter and it keeps the tank at 0 NH3 and 0 NO2 all the time (except after large water changes it seems). What could be going on here? Why if I did damage the bacteria colonies (which I didnt clean the filter this weekend) did only the Nitrite eating bacteria suffer? I will do water changes for the next 2 days but I am away for work for a week and am not sure what to do.
Have you ever seen a French Ninja? NO because they are sneaky.
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