Beneficial bacteria remove ammonia and nitrite- so your bacteria are fine.
They produce nitrate. What you are seeing is normal.
Several ways to reduce nitrate:
1) Less in. If you feed less fish food (especially high protein food) there will be less nitrogen entering the tank.
2) If you are currently using a plant fertilizer, do not add nitrogen. Add the other things. Plants may be able to use the nitrogen best if they have good levels of the other things.
3) Increase removals: Water changes. Larger, more frequent.
4) Encourage the plants to grow faster by seeing that they have the right light, CO2 and the other nutrients that are sort of lacking in fish food. Fish food usually has plenty of N, P and most trace nutrients. Usually lacking in potassium and iron.
API kits usually have a life of about 3-5 years, but some seem to last longer.
GH is the one I have found to not respond after about 5 years. The others seem to give the same results as other kits that I have (several sorts).