Fix your PH. In a DWC you want it to set it to about 5.5 and let it drift upwards to 6.5 before bringing it down again. Different plants may like slightly different ranges of course.
You have described the perfect conditions for root rot. Your water temps need to stay 68f or cooler for several reasons. Nasty stuff doesn't like to grow in cold water, and colder water holds more dissolved oxygen, which nasty stuff also doesn't like.
You can help keep your res cool by adding ice packs. You can freeze water bottles. I drop a couple fishing sinkers into the bottle and tie a piece of string to it to keep it from floating around. Try not to go any colder than 62f. Cheap water thermometer is a must for DWC grows. Moving your air pumps outside the grow room may also help keep the res from building up heat.
Now you will want to read about treating root rot. Lots of good articles out there. You will quickly see advice saying you should add H2O2. Consider what type of nutrients you are using before you add it. If you are using chemical nutes you should be fine, if you are using organic nutes you will want to read up on it a bit more before trying it.
At the very least you should drain your tubs, scrub them, sterilize the air stones and hoses. Snip off the really brown and slimy roots, and keep your res chilled. You may want to change your water every few days to reduce the spoor load.
Also search for the 8 step recovery thread for DWC grows
