I have a 75 gallon tank with a Fluval 406. We recently moved the tank and temporarily put the fish in a 5 gal tank. Drained most of the water in the big tank, but kept all the water in the filter.
Put the fish back in the tank after filling with water and running the filter for a couple days. Then changed out all the filter medium except the ceramics. Checked my water the next day and nitrates were really high. Did another water change and tested again and my nitrates were still 40ppm.
Swapped out 1 carbon packet for a purigen packet. Tested it again and my nitrates are still 40 ppm.
I have a 6" Albino
2 clown loaches about 3"
2 peacocks about 3"
2 peacocks about 2"
Do I do another water change? I know the nitrates are too high but I don't want to stress them by changing too much of the beneficial bacteria. Seeing as I'm just now really getting serious about my fish, I would really appreciate any advice.