I hate EC... I'm an old school guy. Everything is ppm's to me.
Figure all my synthetic feeding by feed NPK per part and measure ml of product to hit my NPK goals.
Metering run off is NOT a good way to meter what the soil is doing, or the plant.
You don't meter run off for pH so why would you for EC or ppm? to many factors to influence the outcome.
You didn't mention pH the pH of your feed solution's or water at plain watering's (if you do that)...
I see some possible pH issues starting - could be related to what i say next but what do you meter your solutions to?
Hmm, Here's a thing that swings all sorts of change in how you feed and the plants grow.
You added Co2 enrichment to your op!
You just changed how much the plant uptakes for needs... It doesn't know what or how much your feeding. It only changed how much it uptakes for the new demands of increased Co2.
You now have to redial in the strain again....
Also, 50% RH and gassing at 1K ppm is too low..
To hold closer to proper dial in's. You should be running a high temp and a high RH - upper 80's for temps and upper 70's for RH. This fits the vapor pressure to the increase in Co2. It now allows the plant to use the gas efficiently - MORE efficiently then you are now. All part of balancing the whole environment.
The best way to control gassing temps/RH ,,, is to use an Environmental controller... I like the inexpensive AutoPilot one.
Simple and effective...
If you can get away from Gypsum and Epson. Far better for you. Many bottled Ca/Mg are enough - period. They are balanced and have the FE to make each work better.
So what are you in? Soil?
Again - Whats the in going pH value of the solution?
I built stand alone buildings to work.. I set them up as "sealed". Keeping in mind the whole thing was going to be under EV control. Lights came on and the gas turned on the meter got it to my set point and the temps and RH climb. Once at my stop point. The EV controller shuts down the gas - turns on the AC and exhaust. This runs till another "set" point and it shuts down everything, turns the gas back on and goes through the whole thing over and over till lights out.
At lights out, she cycles the AC and RH again. Till lights on again.