Andy I just re-read your whole thread.
Once you have carefully checked for pests and have confirmed that it is not pests (eg Red bugs or AEFW's), I would still say that your corals are lacking food. I am a member on at least 5 SPS forums and see similar threads coming up frequently.
What is your phosphate level currently at?
Can you tell me a little about the rocks in your tank? Eg did you have the same rocks in the previous tank? Other than the change of lights from the and obviously change of tank, what else has changed from the previous setup?
Compare your old and new setup for me please:
1. Lights-OLD= ATI T5, NEW=250w Radium
2. Skimmer- OLD=??????, NEW=Reef Octopus XP1000SSS
3. Rocks? etc
4. Sand? etc
5. Mechanical Filtration?
6. Chemical Filtration?
7. Fish stocking?
8. Feeding?
I would actually keep up with regular water changes but increase feeding. The trick is LOTS of FOOD IN + LOTS OF WASTE OUT.
I think your tank is too clean in terms of particulate food. Maybe good liverock with lots of microfauna is worth the hassle with aiptasia etc.
All those tiny creatures are food for your corals. Honestly over the past couple of years I have done a complete u-turn when it comes to corals (particularly SPS). I used to think an ultra clean tank. Now I see more and more SPS reefkeepers especially, saying that we need a bit of phosphate. I think additionally, we need more than that. We need a tank full of microlife, those things will feed the corals as well.
Have a read of this:
Small polyps do capture zooplankton
I found that site only a few days ago. I began searching on the subject matter because I wanted to confirm my idea about coral health and nutrition.
My last setup consisted of 100% Marco rocks. New setup has at least 50% good quality liverock so that I have sufficient microlife in the tank.
Anyway, I will stop my rant for now.