not possible.. if u use mh, most probably u might wan to let us know wad is the wattage of ur mh?
i'm using 1x250watt mh and my tank is 2.5ft depth.. check my last thread.. my tank i keep 1 squamosa, 5 crocea and 2 maxima. all are doing very well with that depth. ya.. so u might wan to tell us wad wattage u using.. and with the amount of clam in ur tank, u got to have a stable ca.. which ur clam might take in quite alot.. and causing ur ca to drop if u don have a cr in ur tank..
hope wad i contribute do help.. maybe more ppl can give comments?