How many days have they been in the system?
When you flood them, how high are you flooding them? For how long?
I wouldn't recommend dropping to only once a day maybe just twice but from my own flood/drain experience I've never went below 3x/day cycle @15mins. As the plants get bigger, you'll need to increase the number of times.
Rez temps are too high.
I top off the rez with just water (if you have RO that would be good), adding nutes when the ppm drops too low (too low depends on age of plants). Shouldn't need to pH water, unless the water you're adding in has some crazy high or low pH.
200ppm is a bit low for 10day old plants, I would raise it to about 300-400. I usually start at 200ppm the first week and increase by 100ppm every week until last two weeks then just keep topping off with just water (no nutes)