What can affect P.E. ?

[PoonTang]

I am looking for some ideas into my recent lack of PE. Everything was fine up until about 1 month ago, had PE up the wazoo. Now I have almost nothing, not even my Milli's, they just look pretty much like bare sticks. At first I thought maby everyone was taking a little break, but it has been at least a month now. Not everything is affected, it seems to be only the Acro family. All of my Monti's, birdsnests, polli's etc are growing great and have great PE.
The Acro, Milli, Prostrata, etc have virtually nothing in the PE department but all have great colouring and amazing growth. At night the big polyps on the tips come out in full force but the rest of the coral is pretty much pathetic. The polyps are there just really small.
All of my parameters seem good and I have increased my WC to 15% per week but its not helping. Running new Carbon and GFO also.
Initally i thought it was related to a possible overdose of Mag or the addition of fresh garlic to the food but both items have been corrected. Also I have looked very carefully for parasites but have found none.
I am open to suggestions and ideas.