CBS question and water chemistry question

[tselios]

Hi. I have a couple of questions. First off, I have a 55gal reef tank with a couple green chromis, couple 4-stripped damsels, a long horn cowfish, and a blue tang. I also have a coral banded shrimp, a cleaner shrimp, and snails/hermit crabs. Yesterday I found one of my 4-stripped damsels got his tail clipped by something. Well, I shouldn't say clipped, but he was definitely missing a big chunck of his tail. Anyone have any ideas on what happened?
Also, another question. I've had my tank for a while and my pH and alkalinity levels are consitantly higher than normal. I haven't been able to find answers on what to do about higher pHs only lower ones. Oh yeah, I use DI H2O. Any help would be appreciated.

 

[duke13]

Regarding your Damsel, I doubt that it was your CBS that got ahold of it. CBS are that quick and Damsels are some of the quickest little fishes alive. More than likely other Damsel is picking on the other. Usually, you should have Damsels in odd numbers, that way the other guy gets a break from the bully.
If your PH is high, I would suggest doing 10-15% water change each week (might consider 2 times for one week, it is kinda drastic so be very cautious). You can buy PH Buffers that can help bring your PH down. Most of the PH Buffer products won't allow your PH to go higher than 83.