no polyp expansions?

Alright so i picked up 15 frags from a guy on craigslist, and theyve been in my tank for about a month, ive got a birdsnest, that is growing like a weed, some green montipora that is also showing great growth and then i get to the acros, they turned solid blue, from green/blue but i never see polyps on them, is this normal? All the other coral i see polyps.. I saw polyps one time out of these guys and thats it, i havent found a good time to feed yet bc of this.. Should i be getting worried? Here are my parameters
Ph 8.2
Trate 0
Trite 0
Ammonia 0
Calcium 440
Alk 12
Mag is 1450
Sg is 1.025
Temp is 78

 

If they are growing well no need to worry.

 

Ok, how do they eat if they dont extend polyps? Or am i just not seeing them? I dont see a growing difference but my friends say they grow everytime he comes over they are bigger, i notice on the birds nest bc it was just a stick when i got it and now there are 13 arms growing off of it but i can say the coloration on everything has gotten amazing since ive had them, the tips of the blue acros are slightly purple and then the rest is blue, butnive got a green that is turning either brown, or maroon and i cannot figure out why...:-/

 

Usually for me when I have had acroporas show no polyp extension it's either too much flow or too little. It's a very hard thing to balance, one tort loves the flow, another with the same flow will not open until I move it to an area of lower flow.

As John posted if they are growing and continuing with good coloration no real need to worry.

 

I have noticed better extension with a alk of 9-10 then my alk of 12 I had a month earlier. Slower growth but better color and pe for myself just my 2cents.