looking for sudgestions

[Whatigot]

I have never had clams in my 24' deep tank, but I have had sps do well (definitely not thrive) near the bottom.
I would def have bought some 250 de's or 400 se's in retrospect.
I actually have some 400's on the way for this reason and am selling my aqualight pro 2x150.

I would think you could probably keep a clam alive on the bottom of your 21' but you will be happy as a clam with 250's or 400's.

Try ebay.