leaffish75,
Sea hares prefer leafy red and green algae. I don't know if it would easily be able to eat the red turf. If you decide to get one, a smaller Dolabella would probably be a better choice than an Aplysia (which get huge). Do you think this alga turn could be Gelidopsis (try searching google images)? Do you have any turbo snails? Do you test your nitrates and phosphates?
Kevin