I'm new to aquaponics and have been researching extensively for the last month or so. I am interested in building an indoor system for the basement initially.

I've read a number of things, from ft:gb ratios and whatnot. As I get close to actually building my system, a number of questions arise:

1. I am initially starting with a 75gal tank, but I'll only put in 40gal of water at first. If I'm using gravel, using a 1:2 ratio, this would imply I need something like 11 cu ft of gravel in my grow beds, or roughtly 1100lbs (550lbs per growbed). More if I fill the fish tank. Is this correct?

2. Just for space considerations, I am planning on stacking my entire system, so it looks something like this pictures which are not yet finished. It currently shows a single tier for the grow beds, but I'm planning on a second tier above the first. All in, it seems like using gravel adds up 3/4ths of a ton of material. (The fish tank should come in at around 450lbs with 40gal of water.) Is this something I can make out of wood and have it sturdy?!? Note that in these pictures, the base is made from 2x2s, all of the plywood is 1/2" and the growbed supports are 2x8s.




3. If I use hydroton instead of gravel, it looks like around 300 liters of material (6 50l bags) which adds up to about 250lbs, or 125lbs per growbed. Does the weight of the gravel make hydroton the only choice? Price difference is about $75 for gravel at the local store vs. $260 to have the hydroton shipped to my house.

4. Is a 5 degree slope on the growbed the right slope to ensure proper drainage?