[Dearth]

Diatom bloom-natural part of the cycle you will get those quite a bit in new tank setups no need to worry they will disappear on their own in time

That sump needs to be redesigned lower the baffles considerably get rid of the sand in the refugium as Mindy said it will cause nothing but troubles in your tank later on. Ideally your sump should be big enough that if you lose power or a return pump dies the sump will contain the excess water draining from your display

While I like your rock work you are really limiting yourself to what you can and cannot put for corals in your tank some minor redesigning of the rock work should make more of it available to put coral on

Other than that it looks good