Everything I can find on Diatoms says it should burn itself out, it uses silicates which I'd guess my rock hard water is loaded with, doesn't seem to require much light as my filter and hoses are coated with the stuff.
I'm really not sure what caused it but I have a feeling it might have something to do with increased PO4 dosage I've been adding. About a month ago I started testing PO4 and getting 0 readings the next day, even when I doubled the dose.. It turns out that Aquasoil absorbs PO4 so I decided to add 1ppm every day, because no PO4 in the water column is bad right? So many people using aquasoil but I can't find any discussion on this really, *shrug*
Also because of aquasoil leeching ammonia I don't add much KNO3, only about 1-2ppm per day. The tank water stays between 10-30ppm (I'd have to calibrate the API kit to know for sure)
I think the fuzz algae might be due to too much iron, I'm guessing my water is already high in iron and I'm using the old "CSM+B plus iron" for trace.
I'm going to cut back on all the ferts and light a little to see what happens.
Plant growth is excellent other than diatoms smothering a little.