Thanks for the picture.
1. Remove as much of the algae as you can
2. Test the water for Phosphate, Nitrate, Nitrite and Ammonia
3. Convert PO4 to P http
/www.water-research.net/Watershed/waterconversions.htm
4. Convert NO3 to N NO3/10 Example 200ppm(NO3)/10=20ppm N
5. Find the ratio of N
10:1 is a phosphate limiting system, 15:1 is a Nitrogen limiting system.
If you have a nitrogen limiting system, then you need to reduce NO3.
If you have a Phosphate limiting system, then you need to reduce PO4.
If you have a high PO4 level >2, you can buy a filter pad to reduce the phosphate in the water. You will see results within 48 hours. There are a few on the market. They are hard to find around town. The one I use is Pura Filtration Pad and will also remove heavy metals.
I'm still working on the NO3. There is a pad for that, but I have not tested it. NO3 not as harmful to plants and fish as phosphates. Some fish thrive in waters with NO3 concentrations of 600ppm+. In fact the air we breathe is 72% N.
This information is used in the study of lakes and rivers and natural habitats of fish and plants and is not used to figure how clean the drinking water. The best level of NO3 for your aquarium depends on the fish in your tank and personal preference.
However, 2+ppm of phosphate will cause algae to grow well. .25 and lower is suggested.
So a ratio of 2.5:.25 is a 10:1 ratio and ideal for plants.
Hope this helps you control the algae in your aquarium.