I would stop using tap water completely. You can buy RO water at your LFS or your supermarket. They even have some places that fill up 5g jugs. You could also use distilled water. Tap water contains all the nutrients your algae loves. And I know a guy that sells RO/DI systems whenever you are ready.

To get rid of GHA: http://www.melevsreef.com/gha.html

Since the substrate contains CC, I'd siphon it with a gravel-vac. Those are a large tube connected to a smaller flexible tubing, and the detritus (and some sand) will siphon out while the heavier CC will stay in the tank.

I wouldn't use any more phytoplankton in your tank at the moment. But for the sake of conversation, can you describe how often and how you are dosing?

Here's my page about feeding tanks:
http://www.melevsreef.com/feedings.html

What skimmer did you buy?