Ok, here goes. I have a 10gal freshwater tank up and running for about 2 months now. All my water levels have been great until about a week ago. I have 5 small Mollie fish since we started. For the last week I noticed that my nitrite levels spiked and NOTHING seems to help. I have performed weekly water changes and cleaned (2 grow to be 1.5", the other 3 grow to be 2") the tank glass and gravel. When the levels spiked I researched what to do and this is what I found and did. I am afraid I did 2 things wrong in the above time frame (1) rinsed the nasty black sponge in 1st filter and (2) my son and I accidentally both fed them days in a row so they got more food than normal.
1) 20% water change and tank was clean on day 1, 2, 4 and 45% change late on Day 6 (today) as per pet store advice
2) added and extra air pump and air stone
3) added Aq salt
4) tried Prime
5) I changed the filter to a 4 stage filter instead of a 2 on day 5
6) added some bacteria (bottle form) today
All levels still show in safe ranges except the Nitrites. The Nitrites are coming down after today's change but are still in stress area at about 3. What can I do or what am I doing wrong. Can someone help me?
The pet store said the nitrite issues the fish could be fine one day and be dead the next without any signs or symptoms. Is this true?