How much water should I add to the Water Farm 8 ?

I got the water farm 8 pack, but im only using 6 of the grow buckets.

The instructions says it uses a 13 galloon res and an 8 gal controller, so does it take 21 gals all together ?

Is the amount of water I put in it very critical ?

Or does it just need enough to be able to suck some water up the pipes to the drip ?

Im not sure how many gallons I should add if to the res if im using 6 buckets.

Please advise.

Thanks

No one knows ?

Come on people...

PLEASE help me out if you have any information on this..

I want to do this grow right. I invested lots of money on this.

THANKS !!