Sponge growth at the base of SPS

[Allmost]

Hello all.
so last night, I saw that 2 of my SPS colonies have an orange and a blue sponge growing on its base, up, and its killing the SPS ! (from base up stinging it, I think)

does this sound right ? is the sponge responsible ? or could it be something else ?

on a side note, I got a camera today will take some pics and post them right after work.

thanks.

some parameters based on tests done last night :
Temp : 80.0 degreess
KH at 7.0 DKH
CA at 410 PPM
MG at 1320 PPM
K+ at 390 PPM
no3 at 0.1-0.2 PPM Salifert
po4 is undetectable based on salifert.

full Zeovit dosing.

 

[MechEng99]

There are some invasive species of sponge. I don't know how they could kill the coral, but I imagine they could block the light or even excrete toxins that could kill the coral possibly. At the best case scenario, the sponge might just be out-growing the coral. Other sponges are pretty harmless, but if you notice the sponge causing damage, it probably needs to go. The link below isn't totally relevant, but it discusses sponges outcompeting other growths for space.

http://www.aoml.noaa.gov/general/lib/CREWS/Cleo/St. Croix/salt_river27.pdf

http://www.biolbull.org/cgi/reprint/175/2/230.pdf

If you want to get rid of the sponge, some types will die just by getting oxygen into their tissues (but then you might have some massive die-off in your tank). You could also try scraping it off, but it'll probably come back. Supergluing over it or expoxying it might also work.