I have been testing my tank every 2 days I know this is a little much. I keep noticing diatoms on sand bed, rock, and glass. My test kit reads Ammonia 0 Nitrites 0 Nitrates 40 ppm thats driving me crazy but I'm going to do a 40% water change tm and hopefully get that 20 or below. I thought diatoms were only in your tanks when ammonia was present? Can you have ammonia when nitrites are at 0?