Yeah actually 1600 ppm may be a little high. Depends on what mix of nutrients? Is is just a 2 part? 2 part plus calmag? Full line of nutes? So just the numbers don't really tell anything.

How long has it been in flower for so far? Also, how are you maintaining the ppm level? And, what do you mean by signs of root rot. Purple stem and yellow leaves are not a sign of root rot. They can be a sign of a deficiency and that may be related to root rot, but they are not a direct sign of root rot. A sign of root rot is a heavy mucuous like coating all over the roots.

Some dying roots is natural and cutting them is just fine. Finally, your veg plant is not budding, rather it's gotten to sexual maturity which is common on an extended veg. Some people don't flower until they see those beginning signs.

Just keep your water temperature down, light out and add some Hydrozyme (am I right about the name? I don't use it but a lot of people do). And answer some of the other questions and we'll see if we can fix up those plants.