i wouldnt advise a sea hare. once it eats the algae, and it will do really quick, it will starve, unless you feed it manually with sea veg, lettuce, seaweed ect... i would find a fishkeeping club instead, they generally have a sea hare that gets passed around each others tanks.
hermits will eat some of the hair algae, but will kill the snails as they need bigger shells.
get a couple of turbo snails for the algae on the glass/rocks, and some nassarius snails to stir up the sandbed.
if you have no coral, cut the lights. i used to run the lights 11hrs a day, and i had hair algae. i cut my lights down to 8 hrs per day (i have corals) and my algae receeded.
you could run your lights 1-2 hrs if you want. your fish wont mind. but if you do have coral id run no less than 7hrs. i wouldnt run less than 7 hrs in my tank.
your other cause could be eccess nutrients in the water, either from overfeeding/dead spots or from the water you use. cut down on the amount of food you add to the tank, add more flow with powerheads, or do more water changes. any one of these will cut down the amount of nutrients in the tank.
you may have nutrient rich water where you live, do a test and see what the parameters are before you add salt. you may need to purchase a Reverse Osmosis unit (RO), to try and get rid of some of the eccess nutrients.
you could add some species of chaetomorph or caulpera, these feed off phospates, nitrates/nitrites as they grow. you will need to keep an eye on the caulpera though. if it rins out of food (nutrients) it dies off and reproduces. and can take over a tank. i cut mine back every few weeks...
another idea is to get some LR rubble and fill all the gabs between your rockwork, to give your tank more filtration, and threrfore better denitrifying properties.
hope this helps...
