water pump cycle

hello all,
how many cycles should i be having in a flood and drain tray 2ftx3ft (35ltr res)with 3 plants in rockwool in it,18 hrs veg lighting? And will time on increase with plant growth?.The guy who i bought the kit off used to run it constant whilst lights were on,til i told him i didnt think that was right,then i shortened it to 15min every hour during lights on.Ive read some things that make me believe that this is too long?,cheers,RM.

rockwool? Not much, maybe 3 times per day for 3 minutes, maybe less. Rockwool takes a long time to dry out.

Thats what i was starting to believe.cheers man,peace.

Do you have hydroton or any other media surrounding the rockwool?

Yeah I should of asked that. If so, add more moisture, say maybe twice as often.