getting a skimmer doesn't mean no diatoms...diatoms are bacteria, not algae...they come bcoz the biological system in the tank is established...n there r nutrients available for good and bad bacteria to strive.
Skimmer can only get rid of 30-40% of undissolved nutrients....
so long as u do water change diligently and clean yr tank walls often...and dose bacteria after water change shd control these diatoms from overwhelming yr tank...and flow is more impt.