dying plants

Im having a problem getting my plants to grow. I have a 65 gallon discus tank that im working on, and i cant seem to get any growth out of the plants. Im using seachem liquid ferts, and my ph is about 7.0. (a little high for discus) My substrait is about 5.5 inches thick with florite and clay. im using a T-5 HO unit by coralife with 10,000K daylight and 6,700K color #3. The only problem im having is getting my Jungle Vallisaneria to grow tall enough to creat over coverage. After this happens im going to run short on light for the plants below. I am using low light plants, such as crypts, and frill, but fear that this setup will still be too bright. im using peat moss in my canister and i have no surface movement. My Co2 and air supply are on a dual timer strip. Air comes on at night will resperation is occuring, and Co2 on during the day. Its been setup for about 6 months with no results. any help would be much appreciated. thanks

the tank itself has been setup for about 6 months, but the light is made specifically for planted tanks. dual 18watt T-5. the box shows the 10 in between the red and yellow waves, which means good for moderate to intense plants. I have 4, 4-5 inch discus. not sure on breed. and a school of 16 cardinals, 2 peppered corys, and will soon be adding more cardinals and some glowlights. My nitrate levels are high, and ive avoided changing a lot of water for that reason. My Co2 is at almost a dangerous level, and i might back of that.