And the nitrates? thats generally the cause of an algae bloom, but you say they're zero. I'm not sure how they could be though, unless you've been doing daily water changes or something.
If my water had enough algae that I couldn't see into the tank, I'd be doing water changes every other day or daily and testing daily to try and figure out the cause.
Instant Ocean will be fine for those but if you want to upgrade look at their Reef Crystals line. I use a 50/50 mix of Instant Ocean and Oceanic but with your list you're really fine with pretty much any good quality salt.
No clam or SPS unless you're pushing 6 watts per gallon. And clams will eat calcium out of your water, you will need to purchase a calcium reactor and switch to a better sea salt.