Originally Posted by killswitch
Green spot is usually from too much light and/or low phosphate levels.
Whats your lighting and photoperiod?.
I've got a Odyssea (spelling?) T5HO fixture with 24W bulbs. It has 4 total but I only run 2 anymore. I have it set on a timer to run for 10 hours a day with a 2 hour break about halfway through.