Originally Posted by doki
I don't use any fertilizers.
My water is low alkaline.
I leave the light on from 7-10 hours a day sometimes I get home from work late however I ordered an automatic light timer from amazon its supposed to come on wednesday.
48 watt t5HO on a 20 gallon high.
That is intense light with no nutrients, hence the algae. Easily fixed. A bottle of Flourish Comprehensive Sup
plement made by Seachem, or FlorinMulti
made by Brightwell Aquatics. It doesn't take much, for a 20g about 1/2 a teaspoon twice a week of whichever. Make sure you get the specific product named, as both manufacturers make other products under these names. And I would stop the Excel.
For the larger swords in the photos, the the left rear corner, substrate tabs would help. Seachem make these, called Flourish Tabs. A package of 10, you use one every 2-3 months inserted into the gravel between the swords. This will make quite a difference. The liquid is still needed, and alone it will help, but these swords, Echinodorus bleherae, are heavy feeders and given your light I would use the tab as well.
I don't know the GH [Alkalinity is the KH] but I will assume you have sufficient for plants. If you have very soft water this might be an issue, but with soft to medium hard it will be OK. I don't see evidence of very soft water (lack of calcium) in the swords in the photos, so I think the GH is probably adequate.