Reassurance please

[SAMSHUNG]

So I'm just starting out with my first sw aquarium (55gal) and I think I've done most of my homework but I'd like to be sure that what's occurring in my tank is normal.

Introduced 25 lbs of live rock to begin my tank cycling 7 days ago and all looked good. Water was very clear I dare say pristine. Started out cloudy after laying down the Aragamax/Live sand but cleared rapidly with flossing. I've been testing frequently and the ammonia peaked a few days ago and Nitrites have begun to register. 0 Nitrates thus far. All seemed normal until 2 days ago when my live rock began turning brown and depositing flaky brown residue on the sand bed. Determined this is a diatom bloom that I've read most new tanks encounter but the transformation from a clear tank to what appears to be a withering tank has got me a little concerned. What's added to my anxiety is that the glass which used to be crystal clear looks like it's got greenish brown spots peppered all over. I'm assuming this may be algae from the green hair algae that is beginning to develop on my live rock. I've been really tempted to prematurely introduce some Cerith snails to take care of things but have managed to govern myself so far.

This is my first post and if I've left out some relevant information please pardon my inexperience on the forums.

Sam