Plant was grown in ebb & flow hydroponics system until it failed, now its in a deep water culture unit.

I noticed the leaves were turning Brown/Grey. I thought this may be a disease so I sprayed Daconcil when needed, but it didn't seem to help, so I thought it might be fertilizer burn, so I flushed the system, but now I noticed the leaves are drying up. So I thought it might be burn from to much light, so I moved the light 2 inches back sideways. but it's still progressing.

Notes:

• Pea Little marvel. (Pisum sativum)
• Indoors.
• Light is 100w 6500K (daylight) fluorescent.
• Light period controlled by timer.
• Light period was changed from 14 hrs to 16 hrs after light was moved.
• next to air vent. (always cold)
• Fertilizer is miracle-gro 20-10-10.
• water has h2o2 in it to keep it oxygenated.
• Air pump keeps water bubbling/moving to keep it oxygenated. (no air stone, just a diy nozzle)