I have a 55 gal. I believe it is cycled. 0 ammonia, 0 nitrites but it has lots of nitrates. I keep changing water but it is coming back. 50% water change every few days to keep up. When I was cycling I did put in plants. Some are looking ragged (pale and loosing leaves). I put in two Seacham nourish tabs. Otherwise there are 5 mystery snails in the tank (+ some pond snails) . Could the plants be causing the nitrates? How do I know if a plant just needs time, or should be removed?