t. crocea mantle troubles

Hello!

I bought a t. crocea at my LFS Wednesday this week. What I thought was
white colorations in the blue mantle are now turning out to be some kind
of mantle rot. Here are some photos (warning: they're rather large! the
last is the smallest at 250k) for reference:

http://www.markhenryenterprises.com/images/clam_1.JPG
http://www.markhenryenterprises.com/images/clam_2.JPG
http://www.markhenryenterprises.com/images/clam_3.JPG

Any idea what's going on and what I might be able to do to fix it? My
tank parameters are good, ammonia 0, nitrate 0, nitrite .1, PH 8.4,
salinity 1.023. It's a 60g tank with MH lighting (the clam was under MH
at teh LFS). I spent 1.5hr slowly drip aclimating the clam and never
allowed it to contact air during the transfer.

I'm concerned because this was apparently starting at the LFS before I
brought it home and it has accelerated over the past 24hrs. The clam is
still light and touch responsive. I have also noticed that some t.
crocea at clamsdirect.com exhibit similar scaring/molting/etc in the mantle.

Any help would be greatly appreciated.

mark h