Last time I tested my tap for nitrates was 2/6/17 and it was 0. I tested my tank nitrates today, both regular and dilution test and I'm getting about 20! That's after a 40% water change Saturday 4/1 and then another 20% on 4/5. So testing at 20 ppm today made me a bit upset. I tested tap and now it looks like it has 5ppm! What do I do to help combat this? My tank is 20 gallon and I have a aquaclear 50 filter. The only live plants I have is pothos roots.