Need Help with Fox and Bubble Coral

[LeanneP]

I bought a bubble coral and a fox coral about 3 months ago at the same time and added them too my tank. Both looked very healthy when I got them but they are both on a slow decline and shrinking in size.
My tank is 2 years, 90 gallon with 10 gallon sump. I have 2 x 250 watt mh lights that are due for a change. I run the mh for 6 hours a day.
My parameters are:
Salinity 1.025
Alk 7.7
Ca 450
Mg 1350
Nitrate 0
Phos 0
I do a 15 gallon water change every 10 days. I had coralline algae growing like crazy a month ago and my alk and mg were a little low but it is stable again and the coralline has slowed down.
I find every few days a lot of my corals look like crap and then they will be fine the next day. I started running some carbon as I thought maybe I was getting a little chemical warfare but it hasn't made a difference.
I moved the bubble and fox last week but they did worse and I moved them back to their original spots. They are at the bottom of the tank in low flow and I wasn't sure the fox was getting enough light but now I am thinking that maybe my tank is too clean. I have been feeding the bubble about once a week and now I am wondering about feeding the fox coral too.
Should I be running my lights longer or is this a feeding issue? I am at a loss as to why they are both not doing well. If I feed the fox coral what is the best to feed it since it has such small mouths. I also notice that they will be open and when I turn the mh lights on they close up and the bubble looks almost swollen but then the next day it is fine. Is this normal?
Any advice much appreciated.
Leanne P