I think your levels look fine, my silica tests at 1.1 and I have no diatoms issues or any negative algae in the tank at all. Your potassium was high now low, that would be the salt, or a potassium additive. Have you switched brands of salt? or changed any additives you use in a while?
I always send my sample in on a monday because I dose prodibio every wed. and water change every friday, make sure you are doing it similiar cause if you dump in something or do a w/c right before sending in the sample I can see a variance.
Your alk is fine, I calculate them saying about 9 in the dkh range, thats great.
C