I never liked mixing any leather with sps, they do release toxin into the water which can trigger rtn. dkh seems to be okay if you are not on any probiotic system, if in any case you are or just started running pellets or zeovit then that could be a major part of your problem.

Also take a sample of your water to the lfs and get them to check your cal, dkh, and mag just to get a extra set of reading. This way there will be no mistakes on you readings.

Frag what ever is alive and tossed the rest, I have very little luck try to save dying sps colonies, but with that said I have done it before.

sorry for the lost, good luck.

what does the dkh have to do with probiotics?

ULNS systems typically do best with a lower dkh, around 7. However, mine has been above 10 for months running zeo with no ill effects. Not a really important value, other than stability. If yours is 11 and stays there, you shouldn't have a problem. A noted issue with high alk and ULNS is tips burning, but that doesn't sound like the issue you're having.

no ill effects?.....wernt you just posting about your polyp extension?:wink:....

This is more what I was getting at before. whether you are intentionally ULNS or not, high alk with low nutrients can cause tip burn in acros and I have found it to cause birdsnests to die from the inside out. So if you're doing a good job at keeping nutreints low, well then alk might be an instigator of this.

probiotic systems like biopellet or zeovit needs to run the parameter close to nsw which is 7dkh 380-400 cal and 1250-1350 mag. in my own experience as well as several other reefers I talked to who run probiotic systems wether its pellets, zeo or prodibio has encounter issue when dkh jumps above 9, usually alk burn will start to show at the tips and or paleness of the coral tissue, then if dkh goes above 10 stn and rtn will soon follow. When that happens, it become an irreversible domino effect. :sad:

Also when running probiotic system, the bacteria stripes potassium out of the water so fast, with the combination of high alk, it will for sure wreck havoc. I use redsea to test my potassium, when I first tested it, it was arond 360ppm since then I've raised it up to 430 using zeo k balance as I found that to be more effective than other products.

Those 2 problems really caused me a lot of headachs in my tank, it caused 3-4 colonies that I had for over a year to die off over the course of couple of days. I did a lot of research finally narrowing it down to those 2 problems. I spent the next week or two lowering my alk and boosting my potassium, it took a bit but everything has finally starting to turn around. It seem that around 7dkh and 430 potassium, even if my calcium is lower everything still seems to be doing well. I had one colony that has been with me from the start that was at the brink of death, I just couldn;t bring myself to toss him out, its now starting to make a slow but steady come back.

if I were you Milad I would give that a try, but remember to go slow. You risk more issues if you drop your alk too fast.

how did you lower your alk?

Well, we're still not sure that no polyps is bad. But by my statement, I mean other than no polyps, my colors are great, growth is as expected and none of my SPS went white :)
Previous tanks ran with alk above 11 or 12 for years, no issues (again, other than PE).

I was dosing BRS Alk with a aquamedic doser at the time with kalk, I took kalk off-line and dialed back my doser about 45 sec, test the level every 2nd day and adjust accordingly. like I said, it took about a week or 2 to finally settle on 7.5 ish, some say it is better to run it even lower but as of now everything is on the rebound so I just left it there.