Sounds like you’ve found a partial fix, with adding cal/mag after if you notice it didn’t do it on its own.
Another thing you could try doing is to partially drain the reservoir before adding your cal/mag. After it has dispensed nutrients but before you add cal/mag let things settle for 2-3 hours (hopefully long enough for the nutes to mix a bit) and then check the ppm in the res. If it’s too high you can take some water out and then add fresh water back in. Since it’s not a complete drain+fill (all 3 sensors not floating) it shouldn’t dose any more nutes.
To do a partial drain/fill this is what I do:
- start to do the drain
- when about 1/2 to 3/4 of a gallon is emptied click pause or press the back button on grobo
- unplug grobo from wall, wait 10-15 sec, plug it back in
- when grobo says draining done (if it hasn’t yet it will in a sec) then click fill
- use some fresh water to do the fill
This will dilute the strength of the nutes that are in the res a bit.
I’d check ppm in res again after that’s settled for a few hours as well. If it’s to your liking then add the cal/mag.
Also, double-check for kinks in #5 hose anywhere or for it to be pinched down by another hose somewhere or by the cap itself, it can sometimes happen over course of grow if something gets bumped.
You might also need to push the drain hose on the inside of the res down further or as far as it’ll go (through the plastic hole in white thing). If that helps then it could be that it was just leaving too much behind and that’s enough to keep the ppm high after a refill. Checking ppm before it goes in and immediately after might help to show if there is something like this happening.
Another thought was the starting PPM of the water – did you happen to get that reading? Maybe it was a bit high to begin with, causing it to skip the cal/mag?