I checked my ppm runoff at my last feeding. I I was going in at 600 and my runoff was 1600. Plants are doing great tho. I do water to about 10% runoff usually...but I might have let my coco dry out too much and now it's got a salt buildup. This is my first time using coco and first time in Hempy so it's been a learning experience for sure.
Nothing like real experience. I have failed my way to success many times. A couple of questions...how much perlite do you have in your coco? Do you water daily?
My personal experience.
I water every morning a bit after lights on. I often run EC .8 to 1.2 or 400-600 ppm. And the plants tell me that's enough. Sometimes higher when they say, "Bring it on!"
I have had good results with 2-3.5 gallon hempy buckets.
I water slowly, say 16oz at a time then wait. The plants will tell you how much they are using in a 24 hour period.
My 2 cents worth, Try watering for a bit more runoff each day, then see if the runoff EC comes down. IMO 600 ppm is not excessive, but the plants are the boss.