A pic would help, but from the description it sounds like BBA or maybe staghorn.
If so otto's or amano shrimp aren't going to help much. Siamese Algae eaters are a better option, as long as you dont feed them with anything else.
However they can sometimes be agressive, so may not suit your tank.
If it's a high tech tank, you may need to look at your Co2 and Lighting levels, particularly the Co2. Try getting up to a stable 30ppm.
I had an outbreak a while ago and I did a 3 day blackout before increasing the CO2.
Blackouts are usually the remedy for BGA (rather than BBA), but 3 days of no lighting seemed to weaken it considerably. Your plants and fish will be fine during the blackout.
Al
Edit:
Actually I also did a large water change and no ferts just prior to the blackout, then another water change after the blackout and increased the CO2. It soon started to die off and eventually cleared up altogether. Dont forget to manually remove as much as possible first ... even if that means removal of leaves or whole plants.