Thriving to basically dead in 3 days?

Growing Granddaddy Purple Kush in 5 gal bucket, I have a nice size air bubbler, clean the bucket every 7 to 10 days, usually add clear Rez but forgot 1 time. This plant was beautiful Saturday, Sunday some leaves started to droop, Monday a lot more, Tuesday all were dropping and the plant was falling over like the branches had no strength. I don't get it. I changed the bucket nutes out Monday, then twice on Tuesday. Nothing has helped. I'm lost. Only thing I can grasp is root rot. Never grown in water before

Those roots look pretty brown which is a sign of root rot. Are the roots slimy? If so it's likely root rot. It's been awhile since I've grown dwc but that's what it looks like to me.
Take a look at this thread if you haven't already

http://rollitup.org/t/guide-to-getting-rid-of-root-rot.347697/

My understanding is that a little hydrogen peroxide every few days helps with this.

Root rot. Not much you can do now, next grow use H2O2 concentrated at about 30% at 1:600 in the res every 4 days . You could also try a chiller to control pathogens.

I figured that's what it was. Didn't really seem slimy. But it still hasn't recovered. I've heard some say to not use hydrogen peroxide. So your saying buy the 30% h2o2, then what mix rate for 4 gallons? Is clear Rez different? Thanks for the help. I have a clone ready for a new bucket so I want to have all my ducks in a row!

If you use organics -dont use H2o2 etc. If you run a steril res (no organics) use H2o2 as suggested. I dont run a large res setup so my needs are minimal, but over the the counter 3% H2o2 is like 79 cents at the grocery store near me for buy 1 get 1 half off. I buy 10 bottles I'm good for months. I use approx 10ml per gallon every 3 days. My res stays squeaky clean and the plants LOVE it.