Algae scrubber will keep your nitrates/phosphates waaaay down.
You don't have an RO/DI unit, but are you atleast using RO/DI water?
Are you using a protein skimmer?
a UV Sterilizer will not do anything for algae.
I would avoid using mechanical filtration for salt water, best option is a sump set up, have the water flowing into some bio balls/live rock, then into where your protein skimmer is. you can even throw a small lamp on the sump with a ball of chaeto macro algae to help with your nitrate/phosphate problems.
The biggest reason for algae growth in a tank is your nitrate's and phosphates being too high.
You can also buy a lettuce nudibranch, they will eat the hair algae.
Also if its a reef tank you're going to want a clean up crew. Get some peppermint shrimp, 10-20 blue legged hermits, and an assortment of 10-20 sails for the 55g. you can also get a brittle/serpent starfish they help a lot with left over food.