Pulsing xenias are dying?

[fishyfun2]

I have a semi-reef tank that is about 4-5 months old. About 2 months ago, I added a pulsing xenia. It was doing great, thriving and splitting off into new corals. Now I have 5 of them, they are all doing poorly. Looks like they are withering! My parameters are the same as they have been for a long time:
1.026
Amm 0
Nitrates <10
Nitrites 0
Ca++ 380
Alk 12.8
pH 8.0-8.2 (hard to tell)
temp 79-80
Do you think Alk being too high could cause this? I also have a hairy mushroom in there, and it seems to be OK. I've had a diatom bloom, getting better. Think I've been overfeeding. I just added a sump and a skimmer, which is pulling nasties from the water. Lightly stocked in this 29 gal, just 2 ocellaris clowns, 9 hermits, 1 cleaner shrimp, 1 sexy shrimp, snails, 1 emerald crab.
Oh, and how to bring alk down?
Please give advice, thanks!

 

[nycbob]

xenia is a hit or miss kind of coral. it could do great for months, then of a sudden declined. i dont think its the alk level. could be water too clean bc of the skimmer.

 

[fishyfun2]

Thank you for replying. I recently read that about xenia, that whole colonies can just die for no known reason, but since I'm new I thought maybe I killed them! They started doing this before the skimmer was installed, so I don't think it's the skimmer. On another note, do you know how to lower alk levels?

 

[my time]

You can lower your alk. with a acid buffer (seachem) but be carefull,watch your ph .I had a xenia colony completey die off also.It started out to be a white patch on the base of one,then got better.3 weeks later,within 3 days they were gone.My tank is a 220 reef
that is about 15 years old.never did know why they died.All other corals are ok.