I love my squamosa and he's pretty easy to take care of but...I have a few of questions and I'll tell you how mine has been doing under PC's...
1) What kind of lighting has the clam been under and for how long??
2) How far will your new squamosa be from your PC bulbs?
3) What color temperature (Kelvin) and what wattage are your PC bulbs? Not all PC bulbs of equal wattage are equally bright.
Your clam might be happy at first and even want less light to begin with depending on what the clam has been through since it left the farm. Clams are often deprived of sufficient light during shipping etc, and need to be slowly acclimated to your tank lighting, and then slowly given more light. It's not just a question of how much light (watts per gal. or square foot), but also how many inches from bulb to clam. Clams will look uncomfortable under too much light or too much current. Make sure you have time to stay home with your new clam and see how it's doing, don't leave it unsupervised under very bright light at first, you don't want to stress it out by "burning" it. On the other hand you don't want to give it less than it wants either. Both situations will cause bleaching and/or damage to the clam and its zooanthellae. Squamosas seem to need less light than maximas and croceas, but still like a good deal of light.
I feed mine cryopreserved plankton as it comes out of the bottle mixed w/ water, or spray-dried plankton blended for 2 minutes with a handblender. 2 or 3 times a week is ok, but don't feed to much!!!! Clams do not like too much stuff floating in their water. Feed LESS than the bottle says, and slowly increase to get a feeling for what they like. With food for clams, LESS is MORE!
I've been keeping 2 maximas, 1 derasa and 1 squamosa under PC's for awhile now. I placed the first three higher up on top of my reef (12 inches from bulbs to clam) & the squamosa on the sand (20 inches from bulb to clam) when I was using 2 96 watt 10,000K's & 2 96 watt "actinics"only to have them all try to jump down to a lower level on the reef to get away from the light. I had bought them all personally, checking out everything healthy clams were supposed to do or exhibit, and they were all kept under MH's in the stores. BUT, I believe they were all subjected to too little less than desirable levels of light before I had bought them and I don't know for how long. Now they all want more light and move around to find more light just as they jumped down when I first bought them to find less light. The maximas seem happy, but the derasa and squamosa walk and jump across the sand to get to brighter spots in the tank. I have moved the maximas back up higher on the reef, and now run all 4 96watt 10,000 PC's, no "actinics" at all, and have ordered 2 250 watt HQI DE lights which should be here next week. It took mine a few months to acclimate to the light I had, and to get to the point where they wanted more, and now they want even MORE, so you need to be patient.
I really recommend getting copies of Daniel Knop's book "Giant clams" & "The Reef Aquarium" Vol. 1 by Julian Spung & J. Charles Delbeek. Both have great info on clams. www.championlighting.com
has LOW prices on books.
Are you planning on getting a bigger tank soon? Your squamosa will get pretty big in a couple of years.