Make sure that what you get is something that you can use down the road to feed the varmints that'll eventually inhabit the system. No point buying something that you're not going to need later. The algae is a good sign.
On another note. The gravel you've chosen is a hair on the large size. You're going to trap alot of crap in there. Not good. You may either want to pull some of that out, and make the bed thinner (less crap trapt), or add some sugar sized oolytic to it to fill in the gaps. If you have any local reefers that you could borrow, or buy some livesand from that'd even be better. It'll make it easier on your burrowing types as well (Nassarius, wrasses, etc)- won't be so abrasive on them and easier for them to move through.
DJ