The friendliest place on the web for anyone with an interest in aquariums or fish keeping!
If you have answers, please help by responding to the unanswered posts.
Simple by testing and performing water changes, if they're at 40ppm do a 50% water change to bring them down to 20ppm. Which is were I prefer to keep the nitrate levels in all my tanks. Depending on bioload, base your water change schedule and amount to get down to those levels.
Do weekly 50% changes, that way the nitrates never become a worry and your fish will be happy and grow well. The easiest and best way to a healthy tank is to just change the water. The rest of this stuff just gives us all, stuff to talk about.