Having the RO
water handy will definately help for the long term but in the short term, manual removal will the the speediest solution. If you get a new toothbrush, the algae will come off quite easily and can be discarded. You'll be suprised how many animals will avoid longer out of control algaes. Once the algae is cropped and managable, the animals should show more interest. That combined with the water changes should fix the problem. Aquiring specialized animals for something like this is not typically the best solution.
What is the main food source used for the tank?