Torches melting away

[oceaninabox12345]

I got a beautiful black torch coral, and a green one at the same time from ASD. I didnt treat them with anything before putting them into the tank. I acclimated them slowly, put them in, and all was well for about 2 months. They even grew. Then the black one started to slowly have its tissue at the base melt away. It happened over around a month and a half. It still extended as usual, but it slowly disappeared. The green one did ok, until the black one was about halfway dead. Then it started to go downhill. Now the same thing is happening, no matter what i do. I have frogspawn, elegance coral, acros, anemones, mushrooms, and everything is doing amazing except for the torches. Parameters are spot on. Torch is in medium/high light, indirect medium flow.
Fish include: yellow tang, flame angel, coral beauty, two clowns, engineer goby, starry blenny, various crabs/snails
Any ideas what this could be??

 

[oceaninabox12345]

Heres a pic

 

[Blackice615]

How old is your tank? When my tank was within 1 year, the same thing happened and I tried a number of torches and hammers

 

[dferran1]

what is the alkalinity

 

[oceaninabox12345]

How old is your tank? When my tank was within 1 year, the same thing happened and I tried a number of torches and hammers

Its 7 months old

 

[Blackice615]

Could be a contributing factor