clam slowly declining, help please


New member
Hi there. I have a maxima clam that has been in my tank since March. I have not added anything new to my tank or changed anything in months, parameters are all good. It is a 125 long, and the clam is on the bottom under a coralife fixture that houses 3 150 watt 12000K and 4 actinics. I've noticed a small decline in the last month or so, maybe even longer, where it's just not extending its mantle fully. Well that was at first, now it's barely extending the mantle at all. It opens and closes daily, responds to light, etc, just does not extend its mantle. I've checked for parasites, and there are no fish or anything else nipping at its mantles or bothering it. I've researched and read, and I'm starting to think it is pinched mantle, but does that sound right since this has been a rather slow decline? When I first got it, it came out beautifully for months, so I doubt it is my lighting or flow, as none of that has changed and all other corals etc, are doing well. I did read that they don't like algae on the outer shell and I have noticed some of that and can try to scrub it off, but is there anything else this could be or does it just sound like PM? Should I try the freshwater dip? and if so, 15 mins or 30 mins, I've read both? I really love my clam and want to do whatever I can to help it, so any suggestions are appreciated! Also, I should note that for a while I was adding some phytoplankton to the tank 1-2 times a week, but have not done that in a while and read/was told that clams with the proper lighting don't really need additional food supplements, but I am planning on buying some of that again, too. Thanks in advance for any tips!