No offense taken here either, I can appreciate a good scientific conversation without reading into it too much. I do think that ammonia/nitrite/nitrate, while they are the most prevalent levels to test for because of how important the nitrogen cycle is, may not tell 100% of the full story. Since diatoms' cellular structure is itself composed of silica, it would make sense to me that excess silicates in tap water could contribute to high amounts of diatoms. As they feed through photosynthesis, I would also bet that the amount of sunlight or artificial light the tank receives plays a large part in the population of diatoms as well. So to me, a large diatoms population does not necessarily always indicate water that is "dirty" or unsafe for fish, when there are other factors that probably affect pop. growth as well.I didn't want to point any fingers at anyone with my above comment. It seems I have offended some but diatoms are related to ammonia levels/bioload and can be very easily reproduced if one wanted to. Has anyone ever kept fry and fed them on the heavy side? Or has anyone done a complete makeover of a planted tank and stirred up some gunk from the substrate? Or has anyone set up a new tank and faced the famous regular diatom outbreak that comes with new setups?
There is ammonia 24/7 in a fish tank, so when one claims they've got zero ammonia, its unrealistic. One can only claim they had zero ammonia at the moment they tested the tank. Ammonia goes up and down, depending on the bioload and efficiency of filtration, tank set up, etc...Diatoms is reality of fish tanks. There's no offence meant. My advice is to consider diatoms as a sign of heavy bioload/possible mini spikes. If that's not the case, great, only time will tell.
Just speculation here, disclaimer that my degree is in business, not marine botany.