Yes, take out the tang......
Give me a break. This has nothing to do with the problem and the tang will be perfectly fine in a 60 gallon tank for a long time to come. Really getting sick and tired of these "tang police".
Seriously, do you people have any evidence AT ALL, that isn't an anecdote, regarding the need for all tangs to have huge tanks?
Triggerobsessed, I suspect any macroalgae in your tank will be dissassembled by your fish in a few weeks. This solution is only effective if one has a seperate tank (refugium) to house the algae. In the meantime, try using granular ferric oxide. It comes under a wide range of names but can usually be identified by it's colour and shape: it often looks like "little clay balls". This product is highly effective at lowering phosphates and nitrates.
Zeolite can help sometimes, as well, but this is best used on an established tank to keep nitrates from rising; it's effect is painfully minimal.
Living sponges should only be purchased if the tank is in perfect condition, as any algae or cyanobacteria growth can smother the decorative ones. Furthermore, feeding the larger ornamental sponges will add to your nitrate problem. So in short, you are right, they are difficult to keep. But the small ones that grow under live rock (I've got tons of 'em) form part of the effective filtration of natural live rock.