My kh is low, so if I don't do water changes for a while the ph in my tank will start to fall. To keep the ph stable in all my tanks between wc I added a little baggie of aragonite.
I wouldn't worry so much about the nitrates as long as you're doing the water changes consistently, you can only do so much about nitrates. Typically it's that you're overfeeding, feeding messy foods way too often (beefheart), filters haven't been cleaned in a while, or just a lack of cleanliness. That would be be my guess.
My kh is low, so if I don't do water changes for a while the ph in my tank will start to fall. To keep the ph stable in all my tanks between wc I added a little baggie of aragonite.