I to am battling high nitrates and can tell you what I have been doing, first off
I would check the nitrates of your water change source, and I have incorporated seachem matrix in my filters which seems to be helping and I am also going to try biohome and I am doing 50%WC twice a week, anything over 50% I would check your ph from tank to water change source to make sure you don't get any wild ph swings
Jeanne
And also I would go with a minimum of 5 discus in that tank rather than 2