EC Increase After Flush

The plants usually tell you how much food they want/need, so i would listen to them. If the EC raises by that much it's either that they don't require as much food (i'm not sure if you follow the manufacturers instructions, or measure to get the correct readings?) or water has evaporated in a higher amount, which would also raise the EC. You mentioned a high temperature, so that could lead to a lot of evaporation, so if possible i would try to keep that in check first. Maybe a chiller might help? Given plants are always grown in different environments i find that i can't really rely on the manufacturers recommendations, but i check daily (sometimes twice) what's the EC in my reservoir. If i notice the EC goes down over time, i know the plants feed more than what i provide, so i add a bit more next time, and if the EC goes up, i know they don't take up as many nutrients and lower it accordingly. I usually then calculate to the difference of what i gave them (i.e. if i gave them 1.6 and they go up to 1.8, then the difference is 0.3, so i take that off the 1.6 the next time and only give 1.3). I do have to say though that i don't have much evaporation happening, as it's not getting that hot here, so that's something i don't have to consider as much, but if i had to, then i think i'd dilute it even more, so i can take some water evaporation into account and don't get a much-too-high-EC value in the res.