WOW..big scare..close call

I have had several fish in a 20 gallon qt tank for some then have beenin the qt for 8 weeks for a single hippo tang 4 weeks..

all were healthy on Monday..I noticed a powerhead clogged (has prefilter)I cleaned the powerhead and prefilter..rinsed in what I thought was tank water(in reality it was RO/DI..Ihad mixed up the mixing bucket.

I didn;t think much of it as there is a filter running on the tank..
all appeared to be okay on tuesday..but on wed my scopas didn't have the normal appetite..tonight I suspected something was amiss..so I pulled out the test kit..ammonia was at .25.nitrites climbing past .5
holy smokes.these fish were going to be released to the maintank on friday..but I decided to bump the date..so rush the fish into the main tank.

there are now 7 reef chromis a scopas and a hippo all getting use the new digs..the chromises are loving the extra swimming room the 110 X offers..the scopas is hovering (the Bristle tooth tomini is letting the new tank mates know who is boss)
Ithe hippo has found his new hidey and is loving his new hole.
that was too close..

I suspect when I rinsed the prefilter in the ro/di I may have wiped out the bacteria..it sure seems to point to that since that is all I did and last sunday when I did the water change all was fine. 0 ammonia, 0 nitrites and 5-10 nitrate
these fish were fine in the tank for nearly 3 months
I though the filter had enough bacteria..

I did that for a few weeks before the filter cycled and the tank becam stable..the problem with qt since it relies heavily on the filter media is, as in this case, care should have been taken when cleaning the filters..normally I reserve tank water and rinse the filter media in the tank water..this will preserve the bacteria..I made the mistake of not making sure I was rinsing in tank water..

definitely will help
I usually keep sponges in my tanks