Flushing is just about what you said. Run PH water through the system once for 2 or 3 days. Then fresh nutes. PH water for a week to flush at end.
Bud looks nice for maturing plant. Get a little scope to check trichomes. Ratshack has one for 10 bucks. Look in the faq's section on tric's, you want mostly cloudy. A few amber a few clear.
OH trichomes are the crystal looking sticky stuff that you want alot of. Close up looks like a golf ball on a golf tee.
You got it going on, just keep asking questions and tuning in. Get a little fish tank thermometer. 68 to 70 is great for your water temps.
Glad to help, just trying to pay it forward till I can get back in on it. I learned alot from latewood.