In a normal 18/6 day the goal is to achieve 20% TOTAL run-off from all fertigation by the end of the fertigation period. Not each time the pump turns on. I use 8 - 3 to 7 minute run times to achieve the 20% goal every day.
I have 6 Hugo rock wool cubes that hold ~1 gallon of nutrients so 6 gallons. If I fertigate them to 20% run-off in each Lights on cycle that is .2x6=1.2 gallons I will have 2 lights on cycles in each 24 hour day. Each light cycle will have 1.2 gallons of run-off 1.2+1.2 = 2.4 gallons or 6 divided by 2.4 = .40 or 40% in one 24 hour period. I don't want to have that much waste every day. My yard can only use so much.
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