Hi,
It's so easy to just dump chemical's in to "fix" problem's, isn't it. Just keep in mind that if you don't take the time to understand the reason why cyano is appearing, then you will be battling this problem again and again.
Have you tried feeding less, adjusting your flow so that there is some across the sandbed, adjusting your clean-up crew, is your skimmer doing a good enough job etc. etc. I would try to pinpoint the root cause of the Cyanobacteria before I would add any chemical's to my tank..... it will kill off a bit of beneficial bacteria as well. Here's some good reading if you have time. http://saltaquarium.about.com/cs/microalgae/a/aa092800.htm
Cheers!