I'm no expert either, but I do consistently get a gram per watt every 100 days or so, for whatever that's worth. I've never used the Lucas formula either, although I have read about it. I use the, let the plant to tell me what my ppms should be method. Water goes down PPMs go up, too much nutrients. Water goes down PPMs go down too little nutrients. Water goes down PPMs stay the same, as goldilocks would say "just right". I am also a big proponent of the SCOTTYBALLS method
https://www.rollitup.org/grow-journals/344359-pineapple-express-g13-labs-seed.html can't argue with his success.
However, where I do feel that I have a little expertise is in the use of a waterfarm, I think there are very few ways to fuck up that I haven't already been through. And, in my opinion fluctuating pH and PPMs coupled with lockout and nute/pH burn, is an over load of nutrient salt build up in the res, and a lot of times on your hydroton as well. If this was my grow, I'd empty and flush the res at least a few times a day for a day or two with ph'ed water, and then run pH'ed water with no nutes until the PPMs got back down to a few hundred, and then start to work the plant back up on nutes, starting at about half strength. But at no time would I give it anymore than it is eating.
I would recommend you put an air stone in your res, this gives much better water circulation than the drip pump alone, which will help combat your salt build up. One of the easily fixed flaws in the waterfarm, in my opinion, is that it has very poor water circulation as it is currently set up, the water layers and allows for things like salt build up and bad pH and PPM readings. An air stone helps with this as well as providing more oxygen to the root zone.
Don't get me wrong, I think the waterfarm is the best way to grow the sticky icky, it's just that it's not as forgiving as soil, it can go south quickly and you must be the constant monitor, not like soil where you can walk away for 3 days and not worry about it. Good Luck!
This is a great thread showing you how to mod your waterfarm to get the most out of it
https://www.rollitup.org/hydroponics-aeroponics/119479-waterfarm-mods-tips.html. Personally, I have drilled out the bottom, added an air stone and drilled a 1 inch hole to run a 3/4 inch pvc pipe to replace the brown pipe that holds your drip tube (easier to take out and clean).