It takes about 7.5gallons of water to fill 1 cubic foot of space, the same amount converted into 5-80 micron droplets would keep the same cubic foot constantly full of mist for 63 days. If you geared the 7.5gal to last as long as the recirculated res you could mist 6 cubic feet (or seriously overmist the 1 cubic foot) for 10 days and "waste" the same amount of nutes As most of the runoff will be unused nutes (mist that missed the roots) you have the option of collecting it and using it on something else, topup for a drip system, dtw coco etc. Reusing a 10 day old recirc res would be risky.