See this is where I disagree. I doubt your corals would be growing if they were recieving way too much light and being stressed. SPS get the majority of their energy from light, not nutrients in the water, so if the light was poor, they wouldnt be growing. Pale corals with good growth is a symptom of many zeovit systems, and like I said overlighting is not the issue for any of them. The idea of having "nutrients" in the system doesnt mean you have dectable nutrient levels, it means that you have enough life in there that is consuming, and popping so that there is only the most trace amount, but available all day. A "nutrient high" sps system should still have undetectable levels, but is fed frequently.
For exanple, I have a 125g with 8 fish. I feed 4+ frozen cubes twice a day every day(8+cubes a day). Most people would probably consider this a "lot" of nutrients to be adding every day, but my po4 and no3 are 0, and my corals are beautifull. I am getting good growth, and good coloration wether they are 2 inches from the surface, or at the bottom and Im using overdriven 250w MH's in lumenarc's.
As far as T5's go, I have researched them extensivley. During my last job I had several hours each day to search the various reef forums and I read every single t5 thread start to finish. I really dont care to link every single one of them, but none of them put t5 and MH on the same scale when comapred properly. Theres always a 20-40% drop in PAR. Ive even run my own tests using a spectrometer at UW to determine how much intensity and what spectrums degrade over time. I know how they preform, and I personally used a 5 bulb t5 unit over a 40g SPS tank for over a year. That having been said, overlighting was never an issue. My colors were amazing(seriously, ask Classclown how my corals looked when I brought them to his house)and I was getting .5inch growth a month. Corals at the top of the tank grew and colored up as well as those half way down, and my lights were mounted 2.5 inches from the surface.
I have seen corals take a while to color up before, and have sen them go brown or pale from being moved. Just give it time IMHO. I agree with everyone else that it is possible that in the particular instance of your purple plasma, being .5inch from the surface, that recieving "lots of light" is a contributing stress factor, but that doesnt explain the rest of your corals. T5 Par drops very quickly as you work your way downt he water column, so thers no way that the light is causing all of your corals to go pale. Sounds like a tank wide thing, not a particular instance(like your plasma).
If it were my tank, id do this:
Start monitoring your alk daily for about a week, measuring at the same time every day. IME alk instability/imbalance is the number one issue for SPS keepers. If your alk/calc regiment appears to be working fine with no swings from day to day, then add a fish and start feeding daily. You have to go slow with ramping up how much you add. Just use a food little at first, then work your way up to what appears to be a "meals" worth. This should keep your nutirent levels low and give your bacteria time to catch up. After a month or so you should notice a difference imo.
Peace,
Jesse