How can there be diatoms when there is no silicate present in the water?!?!

[10" Red Devil]

I am dumbfounded by the sight of diatoms in my tank! I have tested and retested with 2 different test kits a brand new salifert that is fresh and a brand new seatest also fresh. I have tested the tank, RODI, Source, aged artificial red sea salt water, and have gotten zero results.

I feed the tank sparingly, maybe once a week a couple pellets and 1 or 2 shrimp pellets for the nassarius snails. The tank is a 14 gallon biocube that has a refugium, tunze nano skimmer on it. The nano skimmer works incredibly well always pulling gunk. Recently i decided to dismantle and do more water changes. I have done 1 5 gallon water change and then a few days later I did a 2 gallon water change. The diatoms came right back!

There is tons of flow in the tank. The main pump has been upgraded to a maxijet 900 and there is an Aquaclear pushing 130 something at the opposite end of the tank.

The light is only on for 8 hours a day and is a new bulb 70 watt DE halide 14K.

My clown recently passed away so there is no organics really contributing to a nutrient problem.

The diatoms have been around for months now!!

I have included some pics to make sure that what I have is diatoms! Unfortunately my lens is a telephoto so sorry for the poor quality.