Welcome to APC!!
Second, nice tank. I'm a little surprised that your nitrates/phosphates are so low. What are you feeding the discus? I had a discus tank that I needed to do 50% water changes every 2-3 days to control nitrates at 10 or less. What test kit are you using? Could it be old?
Also, I would drive the pH down to 6.6 slowly. Based on the pH/KH table, you should have adequate CO2. I'll upload the table to the articles section soon.
With the higher temps, the plants will metabolise quicker and, therefore, require more nutrients. How much trace nutrients are you putting in?
Lastly, do you really have 12 x 65watts on the aquarium??