Your air temps arent too too bad.. 78 is ideal:) Temps will get worse once summer comes around, but for the moment you arent too bad. Without CO2 78 degrees is ideal.
Your nutrient temps should be between 68-73. At 78 you will get pythium. When it gets hotter it will get worse. A temporary solution is to attach a small computer fan to the lid of ressy so it blows air across the surface of the solution:) This will drop solution temps about 5 degrees on average. That will help you there for the short term. The only disadvantage is that the solution level will drop faster, due to an increase in evaporation, therefore topping off more frequently will be required.
You can also get a Ice Probe
http://www.marinedepot.com/ps_AquariumPage~PageAlias~chillers_coolworks_iceprobe.html
Them lil gimmicks rock and will help considerably:)
Yup your PH is way high bud...
Your PH should be between 5.5-6.1 hydro...6.3-6.8 for soil.. When you say your pH is 6.3-6.8 usually? Do you have big PH swings? Im thinkin so when you say usually:)
PH swings are a huge problem.
Heres what you need to do.
Fill your ressy with r.o. water. Adjust the PH of the plain water. Wait 12 hours letting the solution bubble/mix. Then add your nutrients. (You can start feeding this to the plants at this point, if you cant wait). 12 hours after adding the nutrients check PH and adjust one more time if needed. Adjust in small steps. My 40 gallon ressy's only take about 20ml of ph adjuster each to stabilize it. The key is to allow the ph buffers to do their job before you add in more.
If you correct that stuff you should be well on your way:)
Hope this helps a bit for ya:passingjoint:
GTD