|Byron ||10-19-2011 01:54 PM |
Light is always the issue with algae.
Each planted aquarium is biologically different, but the prime goal is the same: balance between light and all nutrients. If this is achieved, plants will utilize the nutrients and light first (they surprisingly out-compete algae when everything is available); as soon as something is missing or used up, algae will take advantage.
Nutrients are 17 in number, and occur from several sources. Plant fertilizer (which can be enriched substrate, liquid or tablet), fish food, organics from waste, source (tap) water. As the latter 3 especially will vary from tank to tank, the balance has to be worked out for each individual tank, though it is possible to work out generalities to some extent.
For those of us with natural (low-tech) systems, the nutrient most often in short supply is carbon, as CO2. This occurs from biological processes in the aquarium, namely fish and plant respiration (both give off CO2 continually) but more importantly bacteria through the breakdown of organics in the substrate. The latter is the largest source of CO2 in planted tanks. We can fairly easily control most of the other nutrients which can, if needed, be added as liquid or substrate fertilizers. But carbon depends solely upon the tank's biology.
Because algae is so adaptable with respect to nutrients and light, it will readily take advantage of any breakdown in the balance. CO2 will usually be the first nutrient to be used up, and plants simply cannot photosynthesize without sufficient carbon. If light is still present, however "dim" it may be, algae will use it. This is why we say that light should always be the limiting factor to plant growth. Once light is stopped, algae cannot increase even if nutrients are present.
The above is the theory; now to the practical in this present issue. I would reduce the light duration. You can go down to six hours and plants will still manage. I have my lights on 8 hours, and algae is here and there depending upon the tank, but not excessive. But the number of hours depends upon each tank's biology, so simply reduce an hour at a time until you find the point when algae does not continue to increase. It will not disappear, what is there, but it will stop increasing. You have 13w CF bulbs; over my 20g I have two 10w CF bulbs, daylight 6500K. It might not seem like it, but changing to the 10w bulbs might make quite a difference. If it were me, I would do this first, then decrease the duration if still needed as I frankly suspect it might, but not as much. The issue with intensity is that plants will use the light provided everything else is available, and photosynthesize to the max; this means the CO2 will be used faster than under less intense light. So less intense light can be slightly longer in duration than otherwise, provided it is still sufficient to drive the plants' photosynthesis.
Last word on the 10 hour point. In the tropical regions, daylight and darkness are equal all 365 days of the year. But when it comes to the aquarium plants, many of which are not true aquatic but amphibious bog or marsh plants, "daylight" can be direct sunlight or indirect light due to the forest canopy shading it, cloud, overhanging vegetation, etc. The only point about this is the periods of light and dark.