Zoa stalks turning red?

[Reef Quest 11]

Part of my zoa stalks have been red for a little while, not the full stalk either. Any reason why this may be happening?

Recently had lfs run a full panel water test and nothing came up alarming. No ammonia, or nitrite, low but detectable nitrate. 1450 calc and like 400 mag, or something along those lines for minerals. Ph a little low but reasonable alk.

Any ideas? Have a few zoa frags and only these are partially red. The pigment in the zoa flower is also somewhat red, but its a different shade. Could this be normal?

 

[Mike.]

This was happening to mine when they were getting stung

 

[Reef Quest 11]

This was happening to mine when they were getting stung

There closest coral is a blue mushroom thats probably 3-5 inches away and other zoas are probably 7 inches away.

I did see what I believe was aptasia on them once, but I Joes juiced it once probably 3-4 weeks ago and havnt seen any since.

They also fold up wierd sometimes like they are manually eating but I dont dose or feed the tank anything. None of my other zoas seem to fold up like they do.