Media volume displacement?

[Jake Schneider]

Hi Aquanuts!  Does anyone know how much volume displacement grow media causes in a grow bed?  Specifically, lava rock?  I'm trying to calculate how much water my grow bed will actually hold when filled with grow media.  I think it's 40% displacement, but I'm not sure.  Thanks in advance!

Jake

[Jon Nose]

Read somewhere that you can calculate it at 60 % so a 3x8 by 12 inch high (9 inches water) would be

9/12x3x8x7.33x60% = 79 to 80 gallons

[Jake Schneider]

Thanks Jon!   You Rock!  

[Jon Nose]

if you want to be real accurate get a one gallon bucket filled with your media and state measuring water ... heard some types of lava rock absorb a certain amount of water ??

[Jake Schneider]

That's a good idea!  I never realized how much math I would have to do to build this damn thing!  

[TCLynx]

The general rule of thumb is that the grow bed needs about 40% of it's total volume to flood once it has media in it.  Of course that is very approximate and will become less as the roots take up space in the bed.  When figuring sump tank volume needed up you math to figure half the total volume of the grow beds for needed sump tank volume and perhaps even more to give you lee way for the pump and top up valve.

[Jake Schneider]

Thanks TCLynx!  You also rock   

TCLynx said:

The general rule of thumb is that the grow bed needs about 40% of it's total volume to flood once it has media in it.  Of course that is very approximate and will become less as the roots take up space in the bed.  When figuring sump tank volume needed up you math to figure half the total volume of the grow beds for needed sump tank volume and perhaps even more to give you lee way for the pump and top up valve.