At the same site as the bubbler plans, look for "Getting Started" and then "
nutrients" (about halfway down the page). I used that method with my 4 gal, 11 container, pvc pipe/bottle ebb & flow system last year with moderate success. I'm going to try it again this year since last year was my first experience with hydro and I'm still learning what I'm doing!
Basically, she's saying to top up your solution with only pH adjusted water as it goes down, and when you have topped up with 50% of the original volume (ie. 2gals in a 4gal sys) then you let the solution deplete without topping up until it's still above the
pump level (so your pots still stay completely flooded) before you flush & mix a completely new batch.
It seemed to work well for me but for 1/2 the season I wasn't flooding/draining frequently enough for my outdoor sys in the summer sun, and my yield was mediocre. I also waited 1/2 season before I finally bought a combo EC/pH/TDS/PPM meter. Once I had the meter, the 50% method seemed to keep everything in the ballpark so I stayed with it. This year I'm also going to pay more attention to changing to a blooming/fruiting solution when needed, which I waited too long to do last year.