when i had my clam (derasa) in my nano it was open w/ a full mantle all the time. most of the time my nitrates were around 60! lost a few things but the clam loved it... i upgraded to a 30 gal w/ 20 gal fuge. i have a 6 inch dsb in the display and fuge. i switched everything over 6 mos ago. now my dsb is working well and my nitrates are around 10. i actually have more watts on it now, but it doesn't seem as happy- it's still open but not as much. same fish that was in the nano, so no one is picking at it. is the water too "clean" now? just a thought...