All Plants are covered with black(dark brown) substance help

[captainGregor]

I had a standard 55 setup with some javafern, banana plant, some sword. I was concerned about low light (30W) I have ordered 2 55W from AH supply and placed 25 lbs of CaribSea Eco-Complete there to mix with my gravel. Since then I have 110W per 55 g and my plants are NOT doing well. All of my javafern is covered with dark brown stuff, my beautiful banana plant is deteriorating with leaves rotting and getting dark, and I have lots of dark substance covering the glass. This is an established tank and I do not think it is diatoms, although possible. Please advise how I can improve the conditions.
I do 20 to 30% water change weekly. Please advise if there might be a possibility of low CO2 although with 2 watts per gallon it should not be a problem

thanks

[Allivymar]

I've CO2 in my 15g with 30 watts and its fine. Don't think that will be a prob, although I'm sure the plant folks wil correct me if I'm wrong *grin*

As for the black/brown stuff. Hrmm. Is it smooth? Sorta hairy? Does it smell?

Oh, and I'd pull the banana if its rotting in the tank, or at least keep trimming the dead leaves off if you aren't already. If its some sort of algae, you don't want to feed it by leaving the dead stuff in the tank.