Quote Originally Posted by Oliver
Keep in mind that once the grow bed media is in the grow bed, it will displace at least 50% (Hydroton) of the volume of the grow bed (more for gravel) leaving half or less of the original grow bed volume for water. This should be taken into account when sizing your water pump.

If you are using Hydroton as a grow bed media, a good rule of thumb for the size of grow beds is 3.3 gallons of grow bed (minimum) container size for every pound of fish you plan to have in your system at maximum fish grow-out size. If you plan on a ratio of three gallons of water per pound of fish in the fish tank, then this works out to about one gallon of fish tank capacity to one gallon of grow bed container capacity when using Hydroton as a grow bed media.
Oliver, I've been searching for the answer to this and have not yet found it related to grow bed volumes.

Based on the numbers you used above.
3.3gallons of grow bed
1 pound fish
3 gallon fish tank

Does the grow bed hold 3.3gallons of water with the Hydroton or is this 3.3gal capacity empty?

I'm planning out my system and want to ensure I have appropriate sized tank. I'm digging for an in ground tank with internal dimensions of 6'x15' at 3' depth. That comes out to 2,000 gallons for the tank which I calculate that I need 267 square feet of garden space at 12" depth and can handle about 660# fish.
Does that seem right?

I'm using the formula of 1cu.ft.=7.48gal.