Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
You can do two things about rising NO3.
Add less nitrogen.
Remove more nitrogen.
All the other ideas are variations on these most basic themes.
Nitrogen in this aquarium comes from one main source, the protein in fish food. If you had NO fish, just kept on dumping in fish food twice a day the tank would still show rising nitrates.
If you also fertilize the tank by adding any source of nitrogen (KNO3, Seachem Flourish Nitrogen...), then obviously that is also nitrogen being added.
I would cut the feeding to once a day, but do not feed any larger serving. Add kitchen vegetables for the Otos and any other fish that will eat them. Most vegetables have a lot less protein than almost any fish food.
Removing more nitrogen: Do water changes.
Do more frequent water changes. If you removed 3 gallons per day every day that would start to drop the NO3.
Do larger water changes. Instead of 5% water changes, try 25% water changes.
Increase the nitrogen export by growing faster growing plants and prune them. Every trimming is a way of removing nitrogen.