Hard to tell for sure, but looks like fuzz algae.
Originally Posted by Yankee
According to EI this shouldn't matter with a large stock of plants that I have and the photoperiod is at 6 hrs.
EI makes no such guarantee, seems you've misinterpreted something.
Excessive light intensity stresses plants, even at relatively short photoperiods. A stressed plant is unhealthy, even if it appears to be growing fast, and likely to grow algae. I see what appears to be val, crypts, and swords in your pictures - all of which will grow at low light levels, and are easier to stress.
2 x 20W CFLs over a 10G typically provide medium-high light, enough to grow anything. Despite a lot of the light being lost with CFLs. Poor reflectors, poor directionality so light escapes the tank sides instead of being thrown down, and the spiral shape itself causes much light to be absorbed by the bulb.
T5HO has none of these problems, and produces a lot more light per watt. Way too much light in this tank, unless the bulbs are significantly elevated.