The best advice I was ever given was that adding an animal to solve a problem in the tank isn't a solution. Even if it solves the issue, you then have to feed and take care of it like you still had the problem!
A yellow tang will most likely not eat your algae away...even if it does, it still poops and the issue will remain in the tank. Tangs also need 6ft of swimming room...which you don't see in this size of tank. Return the tang and save yourself the frustrations.
When I battle hair algae, and I have before and am doing it again as we speak, I look at where my nutrients are being added into the tank. So, where do they come from? They come in from anything that can decompose, normally food, or our water source. If you don't scrub rock well before adding it, rock that was once live can have things decaying inside of it. Not always common, but I made this mistake at one time. Feeding is a major part in this play. Going from flake to frozen foods can be a big change in terms of phosphates. Then cutting back to feeding is also important, most people think fish need to eat as many times a day as we do! I feed my reef tank twice a week, that's it. Haven't lost a fish in a long long time, all fat and happy. Then there is the water. What is in your water? Who knows, really? My water is different from yours and everyone elses. But it is filled with stuff your fish don't want and then feeds your algae issue. Going from tap water to distilled is a help...but even distilled water still can feed algae issues (this is what I battle), but the switch to ro
water ensures that the water is SO pure that it has 0 TDS
, or total dissolved solids. No solids in the water means nothing can feed the algae in your tank! It means other things that are helpful to our systems, but for this conversation the point is stated.