I don't exactly understand the math, but someone smarter than me laid out the info in a easy to understand way.....
so I get the general idea.
As for the algae, can you post a pic or 2 of it? Black Beard algae?
Do you know the K
- Kelvin rating on the light? How old and what kind of light is it?
The light color spectrum in some warmer tone lights green and yellow are more present, lower K
rating. The cooler tone lights like "daylight" bulbs tend to run up higher in the K
rating. (PAR - Photosynthetically active radiation, is a better way to measure light but not that many people have a PAR meter and more can read the side of the light bulb and see what they have.)
Under 3500K would be bad for growing aquarium plants. It seems someone was able to sustain the very low light plants at 4500K. 5600K to around 7500K would be better for low to medium light plants.
Some bulbs especially florescent will wear out. Lose the colors plants like more and end up with the more yellow green colors, which I guess algae can grow well from.
There are a few other algae management options.
Light is usually a big concern.