Numbers sounds right? (w/ pics)

Here are some pictures..

15 gallon res..
1200 ppm
6.0 PH
Feeding 6
6.1Run-off PH
1160 ppm run-off

Flushed them last week for about 4 days with distilled water. Thursday cleaned the whole system, new water, fresh nutrients, a new oxygen stone, and added Clearex. Temp is 78-80 constant.. fans kick on if the temp goes over 81 and shut off at 79. I'm out of idea's whats to blame.. all ears to hear your 2 cent on this problem.

peace

I would do the following:

1 - Introduce cal-mag + into the mix @1/2 strength
2 - Lower the ppm to 800
3 - Lower the PH to 5.7
4 - Lower the temps 5 degrees

Do that for a few days and see what happens PM me and let me know