Tissue Recession/Bleaching at Acro Tips

[Biokabe]

I've been slowly getting my tank back to the state where I can keep acros, and I thought I had made it. However, over the past couple of days I've noticed one of them seems to be either bleaching or losing tissue on the tips of a few branches. Rather than simply waiting for it to die, I thought I'd ask for help and hopefully prove to myself that I can keep acros again.

First, because pictures are worth a thousand words and I'm already too verbose:

Here's the acro in question, shortly after I picked it up:

It's pale golden with red polyps, but it doesn't photograph terribly well. Also, because of its coloration, it's a little difficult to see tissue loss under the full lights.

Here it was on Monday:

I thought I saw some recession there, so last night I snapped a picture with lights off:

Without the lights, it was much easier to see what was going on, and definitely some recession on the tips.

I don't think there's anything in the tank that would be eating it - I do have a robust population of asterina stars, but I don't think they're of the coral-eating variety. I've seen them all over the place wherever there's algae, but I've never seen them on a live coral. None of my fish are known coral eaters, and most of the rest of the corals in the tank are looking fine.

I think the problem is chemistry, but I'm not 100% certain. Here are my current parameters:

PH: Currently averaging 7.95, with a daytime value of about 8.1 and a nighttime value of about 7.9.
Alk: Currently 10.35 dKH, and where I think the problem is. When I got the acro it was down around 8.5. Without dosing, that value was steadily falling, so I started a very mild dose of 3ml/day, later dropped to 2 ml/day when it kept rising. I discontinued dosing a few days ago after I crossed the 10 dKH threshold, but it's still been going up without dosing.
CA: Fluctuating between 415 and 430 ppm, I'm currently dosing about 25 ml/day.
MG: Currently holding steady at about 1350 with a dosage of about 5-10 ml/day.

I didn't have time to run a nitrate/phosphate test last night; last I checked they were about 1.4 ppm for Nitrate and 0.06 ppm for phosphate, but that was before I did a round of Chemiclean. I'll run one tonight.

Could the rising alkalinity be the cause of this, or some other cause?

 

[SaltISlife]

You sure its bleaching and dying on those tips ? Because can also be confused with new growth. Acros that hrow fast have white tips.

 

[Biokabe]

Pretty sure it's not new growth. Looked at it last night, and the recession had spread further down the tips and was starting to approach the 'body' of the coral.

 

[SaltISlife]

Your nitrates are pretty low tbh. I wouldnt go any lower than 5-10ppm. Mines at 20-40 depending on how much i feed

I have 16 types of acros, i use tap water, no sump or skimmer. And 4 t5 lights two blue plus two coral plus. But theyre high up in the tank where par is around 180-220. Ive yet to meet a acro i cant keep and my tsnk is normally the oposite of what ppl re omend to keep them.. ive found when i brought my same acros to a local store with low nitrates and par in the 90-100 range with those fancy radeon xr15 LED lights. My acros all melted or lost color. The guy cant even keep green slimers.

So it might be because youre too low on nutrients and your lighting may not be up too par. Or you could have too high of lighting

What kind of lights do you have ? Looks like you hsve t5s judging by the pics