Welcome to TFF.
I’ve heard that it’s the amount of lighting not the length of time the lights are on is what’s most important for a planted aquarium. True or false?
Yes, true. Light drives photosynthesis in plants. Each species of aquatic plant has a minimum level of light intensity (brightness) to do this; fast growing plants need more intense light than slow growing species [this applies to terrestrial garden plants, some need direct sun, others shade, etc]. Duration cannot make up for a deficiency in the intensity, but duration can cause algae problems (more on this below). At the same time, plants also need red light and blue light to drive photosynthesis, and red is the more significant. Adding green light to this combination does improve plant growth (even though it is red and blue that drives the photosynthesis); this is probably because a high peak of red, blue and green is closest to the sun, and plants that are green appear to be green because they are reflecting the green light. So the intensity and the spectrum together are significant. Light with a CRI close to 100, or with a Kelvin rating in the 5000K to 7000K range, is best; the "daylight" tubes/led at 6500K are ideal.
Plants also need 17 nutrients. If these are all available at sufficient levels for the plants (and here too each plant species has its own "level" minimum) and provided the light is of sufficient intensity/spectrum for the plant species, photosynthesis will occur. As soon as any one of these factors is no longer adequate to balance with all the rest, photosynthesis will slow and may even cease, depending upon the factor. For example, if the aquarium light (assuming it is of sufficient intensity and spectrum) comes on at 9 am, the plants will begin to photosynthesis provided all the essential nutrients are available. If one of these, say carbon (CO2), gets used up so that at say 1 pm there is no longer sufficient carbon to feed the photosynthesis, it will slow. This leads us to your next question below.
I’m having a big problem with algae and I have plenty of algae eaters, snails, shrimp, etc., and can’t seem to get ahead of this problem. I dose the tank for three consecutive days a month with peroxide in addition. Anybody out there have a magic wand? Thanks, Barb
Problem algae is due to an imbalance of light and nutrients. Duration can factor in here. If the light and nutrients are all available at sufficient levels, all will be well; the plants will photosynthesize full out, and algae will be disadvantaged. In the example I gave above where CO2 becomes insufficient at 1 pm, the light is no longer fully driving photosynthesis in the plants, and algae takes advantage. The same will occur if the light is not bright enough but the nutrients continue to be available--algae again takes advantage. So when the fluorescent tube over the tank weakens as they do with age, and is no longer as bright, we will often see algae increasing. Everything is tied to that balance.
The only way to safely and effectively deal with problem algae is by establishing or restoring the balance. Never use peroxides as this is harmful to the fish. Same with any algicide. They will not work long-term anyway if the balance is not restored. But they do harm fish.
