07-01-2013, 12:48 PM
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A clearer photo would help, can you not zoom in so close? I'm not sure if what I see is brush algae, or something else.
But I can provide a bit of information, now that I know more about the tank. First thing is that with fish in a closed volume of water, there will be organics/nutrients produced continually. As there are no live plants to take these up, algae will easily appear. The light will partially determine which algae, and the more light, the more algae. Various types of algae can occur, it depends upon the specific circumstances. Even those of us with several tanks in a fish room, using identical light, nutrient supplementation, fish loads, etc. find that one type of algae may occur in this tank but no other, and a different type in another, etc. One of life's mysteries.
Algae is not fussy about light, it can use any light. Those with planted tanks know that when the light tube becomes too dim for the plants, algae begins to proliferate. Changing anything, such as light type, nutrients, fish and foods, etc. can spark an outbreak of this or that algae. Algae is very adaptable. It is, after all, the basis of all surface life on earth.
Regular water changes help to control algae, but again this is limited as you can't possibly remove all nutrients permanently. Restricting the light will affect it, but for the sake of the fish you want a regular light period and complete darkness, not something going on and off at odd hours.