I find the angle of the rock under the byssal gland make a difference as does its texture. Too bumpy no good, wrong angle no good (and it seems to differ from clam to clam), etc.

FWIW I have mine in about 50x turnover. Some seem to do OK with glued-in rubble forming a 1" lip around them and others I've had to have the "wall" as high as 3/4 of the clam on some edges (not the whole way around though).

Ya, tank's 24" tall, so 20" water depth and 250's are 7" above water. I'll try find a home closer to the surface for him when I get home. It's Dersa and Squamosa that like it in the sand? I have a little "bay" in the sand that I would love a couple of clams to go in. Was planned as my clam area. But the Crocea want's nothign to do with it LOL

I have read you can put Crocea's in the sand, if you put a rock/shell large enough for it to grab onto under the sand. My crocea that I just got is in the sand, but attached to a very large rock that starts probably 4 inches under the sand and goes up probably 8 inches above the sand. As Tony pointed out, their foot has to have something to fully attach to, whether that's up in the rock work, or down in the sand with rock underneath the sand.

i dont think two Crocea's are alike no matter what we read. they have a mind of their own..some seem to like the sand or BB and dont attach while others will attach throuhg the sand or on the BB tank!