Clams are easy creatures to keep. There are only a few things you need to worry about. Once you make sure of these things are gone from your tank, they are trouble free and long live. They should be beginner level animals. I keep them thriving when I was a beginner and information we had back then, in the 1990 were not anywhere near the amount we have at our finger tips now. Read from well know author rather than any 15 mins video on the net that you can get a dime a dozen (or free)
You need to get a healthy clam to begin with. The clam should be growing, there should be white growth rings on the edge of the shell, the wider the better. When they are growing, the soft tissue inside the shell should be full when it closed. Picking up the clam looking into it, you should not see empty space. Empty space means or equivalent to emaciated clam.
QT your new clams if you have healthy clams in your DT already. QT tank need to be fully light. This is easy, just get a daylight flood light from Home Depo and you are set for short term light in DT. These are the most common disease of clams. Take care of the disease below and your chance of success is almost assure if you provide correct condition and stability. Back on this later.
You need to make sure your tank and your new clams are free of parasitic snails. I wrote an article on how I deal with this pest here This really worth a 15 mins read
How I deal with Pyram snails, the parasitic snails that infected and kill Tridacna Clams
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You need to make sure your tank are free from Pinched Mantel Disease (PMD). I wrote an article on this here. This also worth a 15 min read.
Introduction It was almost 20 years ago when I first introduced the Fresh Water Dip (FWD) protocol for the treatment of Pinched Mantle Disease (PMD). Over the years, many reefers altered the protocol somewhat but, on the whole, it still is the...
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Of course you need stable water and high Calcium and Alkalinity
I always QT my clams before exposed my healthy clams to them. Just make sure they are open well and are trouble free for several weeks. I have several QT tank, and a QT 40 gal reef system that I have running all the time. Dealing with disease in a 40 gal reef is indefinitely better than dealing in a 320 gal reef for sure. Just take my word for it if you never keep a large reef. The main things I QT for is the above two disease, but I am sure there are a huge number of disease of clams out there that I was for fortunate never meet. I know that both of these disease above wipe out my clam collections in the past, only one time each. I learn quickly. I started reefing at a time before the internet and good information were hard to come by. The knowledge instill above are hard won, long and very expensive for me. I hope you pay attention to them. It will save you a lot of grief.
Regarding clams in your tank. They needs stability, don't move them around every 5 mins. If you have enough light, then they should be right on the sand. I keep all my clams on the sand and grew 1 inch Maxima and Crocea to 7-8 inchers no problem. They don't need to attach to anything to live well. You can put them on the rock-work or on coral. Just make sure that it is stable, facing up and leave it there. It will attached and do fine. Within the wide range of light, it is the zooxanthellae that need to adapt to light, not the clam. Within reason, the zoos with adapt to the light level and populate the clam mantle to feed the clam.
Clams that require very high light, upper SPS level are the Maxima, Crocea and Noae. These clams need full tropical sunlight. They often exposed to air in low tide, and nothing to cover the Sun other than the clouds.
Lower level light level, high LPS and Lower SPS level lights, you have the rest of the clams. Of these, I would start with Squamosa. They are beautiful and can be very colorful. Does not require the amount of light needed for the high light one. They grow fast if healthy.
Good luck with your clam adventure.
Lastly, here are few of my clams
