Algae responds best to natural sunlight, but will respond to ANY light. Particularly good are actinic bulbs. With an actinic (Longwave
UV and blue-->purple spectrum visible light) bulb, algae will colonize beautifully and rapidly. However, an incandescent bulb will do (though these are hot and not recommended for the hazards involved) as will regular fluorescents from a fish tank hood (best idea, probably because of the low heat).
The easiest scenario for culturing algae is to get several small rocks or pieces of driftwood with a fair amount of surface area. Submerge these in a shallow tub (4-8") of old *tank* water (which will have nitrates in it) and prop a strong light on top of the tub as close to the water's surface as possible. As algae forms, take out half of the most algae-covered rocks and place them in your tank. When these are cleaned by the otos, take them out and replace them with the other rocks with algae on them still.
Keeping the light on for as long as possible is probably the best idea, though the algae will form just fine if you're keeping the light on for 10-12 hours.
I think that, with the high light, you'll probably get a combination of green and brown algaes. Both are suitable for otos.
HTH
