My GSP is losing its green. Any ideas on what would cause this? Too much light? Flow?
First off, just wanted to say...my first coral was GSP...and it took it FOREVER to turn green again. One trick I've learned in this hobby is that GSP is the canary in the mineshaft. GSP is hardy...but it's also the first thing to start looking weird when tank parameters get off. So, start looking now! It won't die...but it'll quit coming out or turn brown or get slimey or whatever. As much as I hate it, I keep a tiny piece in my two reef tanks just to warn me.
If the GSP is turning brown, you're likely at an excess-nutrient problem or a low-light problem. Most corals go brown in those two cases. Corals turn white (zooxanthallae leave the coral) with an excess of light (and other reasons.) If they aren't coming out at all...it's probably a flow or a really really bad nutrient problem.
I'm going to guess it's a nutrient problem since your tank is new...and GSP can pretty much grow under moonlight (not really, but you get my drift.) What are your nitrates and phosphates testing at? If they're zero, macroalgae may be consuming it before you can test for it (insert here a whole long discusion on organic/inorganic phosphates). You can try cutting back on feeding if you think you're feeding too much, running GFO (granular ferric oxide), or do more water changes. I'd avoid more water changes since your tank is new and the bacteria is trying to sort itself out.
In short, I'd probably just wait it out. At this stage, you're just trying to keep coral alive. Color will come later.
Let the tank do its thing and the rest will come.