Melting Mushrooms

[1boatnut]

My mushrooms appear to be melting away.I had numerous mushrooms that were huge & thriving over the past year. In the last 2-3 weeks,some mushrooms appear to melt right off the rocks and disappear. I noticed a few with something long and stringy coming off and then they would just melt away.
Most of my Ricordias seem ok,but yesterday even my St Thomas shrunk up,but has not melted away.
I don't know where to start.
My parameters are as follows,and these are the only test kits I have:
Temp = 78
PH = 8.0-8.2 (so I know a little low & can adjust)
kh = 161.1 140-200ppm
Nitrate = 20
Ammonia =0
NitrIte = 0
Calcium = 340 (again will adjust)
The only thing of late that I have been doing is my neighbor bought a RO/DI unit and I have been getting my water from him instead of the LFS.
His RO water has been checked at the LFSand with a TDS meter,and all appears to be ok.
Although when I added unbuffered top off water I noticed right away alot of the mushrooms seemed to shrivel up. I posted the other day and was told RO top off water was ok to add just straight,as I used to add PH buffer before.
My other corals,Brain,Fox,Duncan,Acans,Favia,Zoas appear to be ok.
Anyone with any ideas.

 

[tank a holic]

check the new water for phosphates, and copper.
the ro/di should take it out but may not be getting it all, in the meantime go back to the lfs for water
are your lights due to be replaced?
I add buffer to my ro/di because my tap water is low in ph and will bring my tank down
get some wc's going to bring the trates down