Confirmation this ISN'T PMD

[michika]

Hi Everyone,

May I please draw on your expertise to confirm this isn't PMD, or is it? The clam is about 4.5" long and residing under 250w MH bulbs as it has been since it came to me.

Yesterday around 9pm
http://i21.photobucket.com/albums/b286/michika/18432519-1C76-4D4E-B630-6F42715FE06C-26427-00000E94BC9ABC81_zps17fd915f.jpg (http://s21.photobucket.com/user/michika/media/18432519-1C76-4D4E-B630-6F42715FE06C-26427-00000E94BC9ABC81_zps17fd915f.jpg.html)

Today when the lights came on at 2pm.
http://i21.photobucket.com/albums/b286/michika/C7D15AE2-1877-47AB-B9A5-356AADE9DF2F-26427-00000E947C93ABCB_zpsb1da74b3.jpg (http://s21.photobucket.com/user/michika/media/C7D15AE2-1877-47AB-B9A5-356AADE9DF2F-26427-00000E947C93ABCB_zpsb1da74b3.jpg.html)

Yesterday's chems from 9:30pm:
Ph: 8.38
Ca 390ppm
dKH 7.28
Mg 1100ppm
P04 0.02

The tank was dosed yesterday afternoon with Zeoback (11 drops) as per it's regular schedule of every 3 days. New BRS 2-part, dKH and Ca was added to the system during the day(done every 2nd day) and Mg was dosed at night. Last big change to the system was the addition of a crosshatch trigger pair May 15th. They aren't interested in the clams at all.

I have 4 other clams in the system that all look normal and happy; 3 maximas (all about 1.5"), 1 squamosa (~5")

Today is water change day and I plan to change my usual ~50g which is almost 10% of my total system volume of ~550g.

I appreciate and thank you in advance for your time.

Edit to Add:
I forgot to add this since it may be relevant; both this squamosa and the other in the tank both have beneficial commensal shrimp.

[michika]

Moved the adjacent rock to retrieve a fallen frag and waved my hand over top of the clam a few times since its normally pretty responsive. It was a switch in a way, on the third pass the clam suddenly realized there was something above it, sucked in its remaining mantle until the area above it was clear. Then it stretched right out including the gaping you see below.

By about an hour thereafter the whole clam seems puffy with the siphon being particularly extended/open/rounded.

http://i21.photobucket.com/albums/b286/michika/CF402414-D42D-4C87-8755-C67A952D0531-26427-00000E9E28732B5C_zps5d4bfec8.jpg (http://s21.photobucket.com/user/michika/media/CF402414-D42D-4C87-8755-C67A952D0531-26427-00000E9E28732B5C_zps5d4bfec8.jpg.html)

I've kept clams for a long time now, almost a decade, and never had anything like this happen before.

[OrionN]

PMD is a very slow disease that set over many days. I think your clam is fine. It may be irretated by adding alkalinity to the tank. I find that add bicarb quickly into the tank is very irretating to the animalshe tank. Sodium Bicarb solution have very high pH. Sodium bicarb cause a quick increase in pH of the tank.