diatoms are usually caused by one off three things......old bulbs can sometimes be the cause.......excess nutrients, either from a cycle or from overfeeding can be a cause...... and finally, poor flow, all of which are easy fixes.....
I would have to agree with madreefer about the clam......I put two squamosas in my reef about six months after it being re-setup after a move....both died within a couple months.....this scared me away from clams for a while then I tried again after the tank was a year old and every clam I've added has done well(save one.....not sure what happened to it?)..... it doesnt matter if the rock was cycled or not, if the rock hit the air then its basically a brand new tank..... one month is to soon for a clam IMO
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260g mixed reef, 105g sump, water blaster 7000 return, Bubble King SM 300 skimmer, Aqua Controller Jr, 4 radions, 3 Tunze 6055s,1 tunze 6065, 2 Vortech MP40s, Vortech MP20, Tunze ATO, GHL SA2 doser, 2 TLF reactors (1 carbon, 1 rowa).
http://www.canreef.com/vbulletin/showthread.php?t=50034 . Tank Video here
http://www.vimeo.com/2304609 and here
http://www.vimeo.com/16591694