The type and timing of irrigation in a hydro system should be determined by the medium used. The denser the medium, the longer it will retain water. But that means less room for air in there. That's why dense media like rockwool and coir fiber are used, because of their good water retention, as well as the ability to maintain sufficient amounts of air even when wet.

For dense media, a drip system is best because of the water column that goes downward in a cone shape. Dripping into looser media like growrocks doesn't work as well because the water column is more like a straight-sided tube.

For growrocks, it's best to flood and drain. That pushes all of the stale air out of the rocks, and sucks fresh air in.

For no media, as in aero or NFT, the roots are bathed constantly.

For each system, you should experiment with the irrigation timing to find the optimal for your medium, so your plants always have everything they want.

HTH

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