I have been using Jungle 6-in-1 testing strips on all 5 of my tanks for a while. Three are fresh and two are marine. When checking the results, all 5 strips show an insane amount of nitrates. I use only R/O or D/I water and am very careful about overfeeding and such. Is there anything in my water that could be giving me a false reading? All other parameters are find and all my fish and inverts seem to be thriving? Should I try another testing method - what's the best?