My two small plecos still haven't taken to algae wafers, so how do I get green algae to grow? Does "green" medecations kill it? I get plenty of brown algae in my 18-gallon, but no algae period in the 20 (where the small plecos are). Both tanks are lighted with a pair of 48-inch flourescent bulbs in the standard "cool white" color. Will just replacing these bulbs with "grow-lux" or aquarium bulbs help? Thanks.