[michika]

I feel like I should say something about 175w MH lighting. I use 175w MH on my 24g cube. Yes my cube is 18" deep, but I do find I get good coloration throughout the different levels of my tank. Of course the higher the frag the more "intense" the coloration is. I feel I get good coloration from my lighting, but I attribute it to both a high bulb quality, and having chosen a spectrum that works with my existing lighting. Like Reef_raf said, 175w didn't work for him, but it worked for me, so its all about what works for you.

Mik, what everyone is saying is that 175w MH isn't necessarily the best, and that it has worked for some, and not for others. Before you go looking at upgrading your lights or anything, we're saying you should focus on your water quality.

From what I've been following here is what I would do if I was you.
1) Get my water parameters under control and maintain them for at least 3 months before adding anymore SPS.
2) Step back and reevaluate your set up. How are you existing SPS doing, what about your livestock. Are you seeing growth and color in your SPS? Are you fish thriving? I know you take photos of your setup, so consider keeping a "photo diary" of your existing frags, and see if they grow, color up, or brown out. From there you should be able to ascertain where you need to go next, whether its a lighting upgrade, or something else.

To answer your original question about SPS and flow, this is how I understand it works. Flow helps because it gets the SPS, and LPS to extend their polyps. The heavier the flow the thicker branches seem to appear in SPS because they must withstand the force of the flow. SPS are found on few different types of reefs, each with their own flow and ebb patterns. Flow helps reproduce the natural environment, it provides circulation through branches, and even brings nutrients and disposes of waste. More flow is better, to a point. In my experience, and my tank, my sps like to wave a little, but its just that my experience. Pick up Borneman's Aquarium Corals book, its invaluable in helping you educate yourself on what your keeping, and what we know about these creatures.

A phosphate reactor, using a phosphate remover, will only remove phosphates, it would necessarily give you better coloration.