Q: Water calculation: tank size, gallons/day, etc

I've not grown for a couple of years because reasons, and I'm wanting to use an automated configuration with 6" rockwool blocks. I don't have a good handle on watering amounts. If I want to have a reservoir for a week, what size of reservoir tank should I calculate under 1000 watt HPS , I'm coming up with 1.5 gal/day/plant or 262.5 gallons for a week for 25x plants... does this jive with what people see in real life?

Math I think is correct:
Worst case if I calculate the max capacity of a watering session would be for block dried to 30% moisture:
A 6" block is 216 cubic inches
216 * 70% moisture = 151.2 cubic inches of water block can absorb
151.2 * 1.15 (15% runoff) = 174 cubic inches
174 / 231 (cubic inch/gallon) = .75 gallons / plant

Watering twice a day for a week = 7 days * 2x water/day * .75 gallon/water = 10.5 gallons / plant / week

One figure that has always served me well is 5 gallons per day for every 1kW light.

That was with flood and drain, large grows with CO2.

Renfro said:

One figure that has always served me well is 5 gallons per day for every 1kW light.

That was with flood and drain, large grows with CO2.

Click to expand...

Thanks! You confirmed I was in the correct ball park, under my calculations 4x plants per light I'd use 6 gallons per light, which was calculated at worst case.

The math is really about respiration and that correlates to canopy area and lighting wattage. So if you know the amount of wattage you intend to run (thats determined by the canopy area) then it's easy to estimate the worst case (full canopy peak growth) based on my experience.

They will drink at different rates of course. Usually around week 2 or 3 of flower they start to drink rapidly. Around week 6 or 7 they suddenly slow down on the drink and they keep slowing down as they ripen.