[hoppycalif]

Glass tops do collect condensation, in my experience, so they do attenuate the light at least a little bit. What I used to see is a glass that was just dripping with water every morning, but the water evaporated soon after the lights came on. That means a residue of crud on the glass which also attenuates the light. I got tired of trying to get rid of the crud, so both of my tanks are now open to the light fixture. The condensation I get inside the light fixtures has not yet caused a problem for me.

 

[hoppycalif]

With the amount of light you have you need to dose fertilizers more often than weekly. The plants will quickly use up the weekly doses, then languish until another dose is provided. The EI fertilizing method uses 3 times a week dosing, or even daily dosing, with lower doses, as I do. Other methods, such as PPS Pro use daily dosing. Also, be sure to dose adequate amounts, either per the EI method, which intentionally overdoses, or per the PPS Pro method which tries to more closely match doses to needs.

It is very hard to provide enough concentration and keep it consistent enough, using a DIY type CO2 system in that size tank. If you can afford it, go to pressurized CO2, and you will immediately see better plant growth results.