I use a 1.4W 445nm m140 to deal with my DTs when issues pop up.
Anything in the links DTR posted would be perfect.
If you plan to do long sessions of aiptasia blasting, I would definitely suggest getting some spare batteries.
I see 2 of the sellers listed above will include some spares for a reasonable fee.
And safety glasses are not an option they are a must!!
If you can't get them included with your laser purchase,. then there are some availble here:
http://laserpointerforums.com/f39/fs-laser-safety-glasses-445-405-532-a-80643.html
at a very reasonable price.
and grab more than 1 pair .. your family and friends will want to watch
pay attention to your duty cycles, and stay close to 1.4W and you'll have a pest killer that will last you a good long time ..
A few other quick pointers:
Make sure your water is crystal clear, run carbon in your filters if needed.
Turn off your sump, it keeps the heat from dissipating, and allows you a chance to siphon off any "debris" that may kick up into the water column.
FOCUS, it is critical .. It makes the difference between this being a chore, and something you look forward to doing
a quick search on youtube and you'll see the difference between a beam that is focused and one that is not quite perfect (30 second kill vs. 3 minutes).
Oh, and I almost forgot. Be prepared for everyone within 3 states of you to ask you to come over and zap their problems away..
Hope that helps...