Oh yes, how did I miss that you wrote about excel already. Sorry about that. After rereading, it sounds like you just started dosing ferts? Perhaps give your plants some time to catch up to your fertilizing regimen?
Remember, the proper "balance" for avoiding algae is having enough fertilizer and co2 to match up with the lighting. Darkblade's Primer to planted tanks
. Even though you're using excel, it isn't as effective as plain co2
. So if you're short on fertilizer and co2, and you have too much light, you're asking for the algae.
Things you could probably try with aims of reducing light and/or bringing your other factors into balance..
suspend the light higher so there's more distance between light and substrate.
cut off or cut down one of the lighting periods -- especially the night one. if you have ambient light around the house or sunlight coming into the room, don't underestimate the ability of that to grow your algae despite your shutting off the lights. I used to turn on my lights later in the day so that I can see my tank later into the night, but in a decently sunlight flooded room, there was plenty light to grow algae it seems. So, while the plants weren't growing during lights off, the algae was growing double time.
wait a week and see if it does better now that you're adding ferts. actually, you have a dirted tank. how new is this tank? Some will argue that newly dirted tanks don't really need the extra fertilizers -- especially if your plants are root feeders. It "seems" that your plants are growing decently and presence of algae on the glass in addition to the plants would point to more than just a plant deficiency.
So, this may also point to the final cog.. a co2 shortage for the amount of light
If you're adamant at staying low tech, then try your hand at diy co2 with yeast and sugar instead of excel or even in addition to the excel.
Hang in there!