Yes, agree with Robby.
Very important that you make sure there are NOT any things like NitraZorb in your aquarium or filter. The confusing part for beginners is that it makes sense for them to think: If nitrites(NO2) are bad and I can buy a chemical that removes them, then why not? I'll just remove them until my filter is working again.
The answer, and the reason this doesn't work is that the chemical will indeed remove the nitrites, leaving no food for the N-Bac population (the second of our beneficial bacterial species we work so hard to grow in the filter) and it will never grow. Then when the chemical stops being there, for whatever reason, the nitrite(NO2) level will suddenly skyrocket and kill the fish very quickly, if not almost immediately.
Its very important to grow and maintain a healthy biofilter population that matches your fish population. This can only be done via fishless cycling or fish-in cycling and usually -without- other chemicals used in the process, other than conditioner for the tap water.
~~waterdrop~~