Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Do enough water changes to keep the NO2 under 1 ppm. If the current level is 5 ppm, then I would do 2 water changes, 50% each AM and PM today, then repeat tomorrow. See how much the NO2 comes back up. You may have to do more or larger water changes.
Add sodium chloride (table salt, kosher salt, picklling salt...) At the rate of 1 teaspoon per 20 gallons. This is a very low level for plants and salt sensitive fish, but is the right dose to protect the fish from Brown Blood Disease.
Nitrite removing bacteria (Nitrospira) grow more slowly than the ammonia removing bacteria. So, if something happened to some of the bacteria, the ammonia removing bacteria would recover faster. You would see some lingering NO2 until the Nitrospira catch up.
Water changes do not remove the bacteria.
Adding chloramine with dechlor is not a problem; rising NO2 is a problem.
A product like Prime that locks up nitrite is a good idea. Read the label for dosing.
You can buy a bottled product that has Nitrospira species of bacteria to speed the recovery. Read the label, make sure it has Nitrospira. Do not waste your money on anything else.
Add more plants, especially floating plants, and make sure the plants have good light and a source of carbon. Floating plants get CO2 from the air.
You are doing good to feed less.
Perhaps another gentle vacuum of the substrate can help. I would not disturb it too deep, though, unless you know there are dead plant roots in there. Just sort of tickle the upper layer to remove the most recent fish poop and fallen food.
Go really easy on cleaning the filter media. The bacteria live on the surfaces in a bio film, but at less than a month old this is not well established. I would slosh the media around, not wring it out at all.