If the coco is consistently wet, and youre not overfeeding it'll take several weeks for salts to accumulate to a point where they become even a minor issue. I now water to significant runoff once every two weeks or so, sometimes longer. The rest of the time nah its barely a few drops if any. 5 to 6 feeds a day. The more you feed the less runoff you need. Simple as that. Its the drying of the medium which causes nutrient spikes.
I cant even imagine watering to 20-30% runoff with 6 irrigations a day. Thats a massive waste of nutes and water. Once the coco is wet, its wet. Maximally saturated, its not going to get any wetter by pouring another gallon through it and its the presence of water which prevents nutrient concentration.
Like I said tho, all of this is assuming a dialed system, appropriately sized pots, etc.
Since this is an older post I would like to give a update.
I have run 4 grows since my post about my vertical grow, have not run anymore verticals but have run two SCrog's and two using the net to support the buds.
On my second SCrog I reduced the run off to the point that I would maybe get a few drops of runoff. At the end of each rez with one to two gallons remaining in the rez. I add 2 to 3 gallons of pH'ed RO with Cal/Mag and Epsom @ around 0.25 to 0.3. I do a flush running one to two minute run times till the rez is empty. Then refill the rez with 21 to 24 gallons of fresh nutrient solution and start the process again.
My grows have been stronger and the yields larger with very little tip burn. I have been running this now for three runs and on my forth run at present using this method. My last run in a 4 foot tent was Mimosa EVO and i achieved my first two pound harvest.
At present I am in the second week of 12/12 with Cookies and Cream regular seeds, all 5 plants were females.
Using the same rez system I am doing 5 cycles, first and last are 75 seconds and the other three are run at 60 seconds. I get not runoff in the first 4 run times and get just minor runoff from the last run times. I am still doing my end of rez flushes and all is well to date.
Pic from yesterday evening. light have been raised to 26 inches and the intensity of the lamps are set at 8, may raise that to 9 this week.