melissa
I've got a 30 long mixed reef tank as well.
Although your's sounds a little more stocked with inverts, fish and live rock than mine, still somewhat similar I'm sure. Most everyone experiences some algae growth - trying to figure out the cause can sometimes be tricky ?
I don't want to repeat myself here, but what are your water test readings ?
Specifically your 30 tank's
pH
Nitrate
Phosphate
What is your lighting type and lighting schedule ?
What type of fresh water are you using for top offs and mixing salt ?
Water change schedule and amount ?
Clean up crew ?
A protein skimmer as said above, can sometimes reduce much of the organic wastes that collect in our tanks over time - especially if we tend to overfeed and have large numbers of waste producing creatures.
Personally I like running my skimmers - but again as said above, they are not at all "necessary" to have a sucessful reef