Nitrite will not go away

[WilliamWeaver]

I have been changing over 75% of my water 2 times each day. I have been doing this for over 3 weeks now.

The nitrites are over 5 ppm each time before I start and over 6 ppm two hours after the change. I use a liquid test kit.

I have a 350 gallon tank. The water changes over 6-7 times per hour..

I have a 400 GPH HOB bio filter and an FX6 canister filter setup as a bio filter. I have a 2100 GPH wave maker..

Each time I change the water I put in BB and chlorine remover for a 500 gallon tank.

I have a 14-16 inch bass that does not show any signs of distress.

The ammonia is at 0 ppm, the nitrates run at around 20 ppm.

[Riyadh]

Is it possible that the test kit is expired?

[WilliamWeaver]

Brand new test kit.

[Boundava]

A couple questions:

How long has the tank been set up?
If not long, did you cycle the tank?
When was the last time you cleaned the filters?
Have you tested your tap to see if your nitrates are coming from there?