I have some algae growing on my swords and one some of the floatimg plants.
A few months ago I added the much brighter light and expected some algae to show but with the huge top cover it never did ... until now. About two weeks ago I took out a very large part of the duckweed and pennywort to let more light to the bottom of the tank. The fall season change has also resulted in some direct sunlight which, in the spring, didn't affect much so I expect it is a combination of factors. The direct sun only lasts about a month and is only for a short time in the late afternoon.
Fixes will include covering the glass lid with strips of paper to reduce the intensity of the light while the surface plants grow back, being more regular with the liquid fertilization and reducing the photo period by one hour. I'm not worried about the direct sun as the algae is not only on sunned parts of plants.
I included a shot of one of the leaves of my sword. There is a trumpet snail there that appears to be munching on the algae, which is interesting. I noted other MTSs on other leaves doing the same thing. Typically those guys are not on any of the leaves so I assume that it's the algae they are after.
Now I get to join the "I have algae" club!