If its showing nitrite, looks like the ammonia has being converted... sounds like a mini cycle maybe.
a waterchange 50%-70% would probably be the answer
Someone asked your tap ammonia? What were the results? are you using a new dechlor? there weren't lots of dying leaves? any fish/snails/shrimp missing? You sure you used enough dechlor? You didn't rinse the filter in tap water?
a waterchange 50%-70% would probably be the answer
Someone asked your tap ammonia? What were the results? are you using a new dechlor? there weren't lots of dying leaves? any fish/snails/shrimp missing? You sure you used enough dechlor? You didn't rinse the filter in tap water?

and 2 externals suck up the bits the corys kick around.