New Clam

I bought a new clam,a 2" squamosa(I would have got a maxima cause they're both 25.99,but teh squamosa was the biggest. How long does it take for them to get accustomed to a new tank?I know I have enough light.Also,how do I get rid of these pesky diatoms on my sand and rock?
Well I just added some clams to my tank yesterday and they are opened really nice today. I am slowly working my MH over them. It is on a sliding rail so when I add new clams I work them into my lighting slowly over a week or two. I also feed some pytoplankton to them. They clean it from the water fast.