For a full coli,
The 1200 liters (300 gal) of perlite-vermiculite that a coliseum holds will hold up to 30 percent water or 360 liters(90 gal) of water or solution. So the grower can see that the coliseum medium has 120 liters(30 gal) of solution moisture retained, when the medium is watered again.
If we were using a peat-perlite mix of 50 perlite-50 peat (sunshine mix), this watering cycle would change. 50 per/50 peat will actually hold up to 50 percent moisture content. So the 1200 liters(300 gal) will hold up to 600 liters(150 gal) of solution.
1200 liters of p/v holds 360 liters, and 1200 liters of perlite/sunshine would hold 600 liters.
half a coli holds half as much...
this is the denotative answer..
of course..how dry is your media..or how much time will it take to wet it, etc..
the first time
from experience, the initial set up is usually 2-3 times the weekly volume.
One thing that really helps hydrate dry media is time..so water for a few minutes, then off for 10-15 then water for a few..etc. to give the media a chance to hydrate. One needs to water the media to dig the transplant holes out so they don't cave in, so start by watering till runoff is achieved..then transplant, and water until your runoff ppm reaches the desired level. If you dont allow enough time for soaking the first day, then make sure you reset your reservoir and water one more time the next day till good runoff is achieved. remember we are setting things up for the time to come so lets do it right.
a little less of an exact answer, but more realistic i hope.