I used the Aquamaxx TS-2 sulfur denitrator as well and liked it a lot. I recently pulled it off line (i clogged one of the lines and had to clean it up). I have yet to put it back online since my nitrates are low.
I also use a lot of marinepure in my system including the 4x4x8 block which seems to keep my nitrates about 1-2.
For a FOWLR though, 20 nitrates is nothing, even 80 won't have a negative effect. If i was in your position i would either carbon dose (vodka / vinegar as mentioned above), add marinepure or vibrant *(im still testing vibrant but so far so good).
I also use a lot of marinepure in my system including the 4x4x8 block which seems to keep my nitrates about 1-2.
For a FOWLR though, 20 nitrates is nothing, even 80 won't have a negative effect. If i was in your position i would either carbon dose (vodka / vinegar as mentioned above), add marinepure or vibrant *(im still testing vibrant but so far so good).

