[GpsFrontier]

hmm.. youre math is a little wronga gallon of water weighs roughly 8.34lbs, and the entire container would be 6 inches deep but if it was filled all the way to the top, it wouldnt leave much room for good aeration, so even if it was filled up to the 6 inch point, it would not weigh anywhere near the 1400lbs of gravel, and the 8x4 by 4 inch area will only weigh roughly 600lbs...

I was just going by the measurements you gave on your system design. If you drop the water level to 4 inches, that will cut 1/3 the water and weight. As for the weight of the water, for some reason I still remember from way back when, when I worked as a courtesy clerk at a grocery store, a gallon of milk weighed 9 pounds, and I did say water weighs ""approximately"" 10 pounds. But going by your figure of 8.34 pounds, and cutting the water volume by 1/3, it does come out to a little under 700 pounds. Although I was already weary about using only 6 inches of water for such large plants as tomato's, peppers, beans, peas etc..

P.S.
While I'm thinking about it peas are legumes, and legumes secrete root extrudes. These root extrudes could cause problems when the roots come in contact with roots from other plants.

the plants would be setting in the holes, the lip of the pot would rest on the top surface while the rest of the pot sits in.. so they could me lifted out from the top.

It sounds easy enough to just be able to pull the baskets up through the holes, but if you haven't grown them that way before, you would be surprised how fast the root system grows. If the baskets you use have slats on the sides of the baskets, the roots will quickly grow through them. Making lifting the baskets out of the holes without damaging the roots impossible the bigger the plants get. Just look at the root mass from my pea plants (picture attached), that was from only 4 plants, and completely impossible to lift the baskets more than an inch up through the holes without cutting the roots with a knife.

a question for people that have built such large deep water culture systems... about how long does it take before the solution has to be changed?

There are quite a few variables, and there is no set time. That is also one of the difficult parts when you are growing everything from small to large plants in the same water culture system. The individual plant needs cant really be accommodated. But small plants wont drink up nearly as much water and nutrients as the larger ones will. In contrast just one of my broccoli plants could drink as much as 2 gallons of water a day when it got big, but I had 8 lettuce plants and they would only require about 1 gallon a week (all of them combined) when they were big.

The bigger the plants the faster they will take up the nutrients, and thus leave the nutrient solution unbalanced. But I generally let my plants go between one week, and 3 to as much as 4 weeks (in some cases) between nutrient changes. But the amount of water volume in comparison to plant size and root mass is a huge factor in how fast the nutrients are depleted from the water. In the cases where I let it go for over two weeks, the plants were not full size, or there was a large volume of water in comparison to plant mass. General rule, large plants like tomatoes need a "minimum" of 2.5 gallons of nutrient solution per plant, medium sized plants like herbs or peppers need a "minimum" 1 to 1.5 gallons per plant, and small sized plants like lettuce need a "minimum" .5 gallons per plant. If you use the minimum amounts, you'll need to change your solution often like every week. If you use double the minimum volumes, you can probably go two weeks fine. If you use double the minimums, and your plants are less than half size, you can probably go longer than 2 weeks. But when you have various types of plants, and of all different sizes, as well as in all different stages of growth, there's no real guidelines to fallow. It's just more of a guessing game, as well as trial and error.

since this will be set up in a basement, im thinking of installing a float inside the resovoir, that when it drops below a certain point it will light up an led which will be wired upstairs, maybe in my living room so that i wont miss a refill

This is a good idea, although I would just use a float valve connected to a water line. Let the water line automatically fill the reservoir to the desired water level automatically. It won't provide water circulation to the main reservoir, unless you use a secondary reservoir as well. But it will keep the right water level. You can get a simple float valve at wal mart for about $4 (it's a replacement float valve for swamp coolers), or anyplace that sells swamp cooler parts.

see, the trouble im having is when i look at other peoples systems, theyre usually small scale for single, or a small group of plants, none of them really seem to be tailored for this size..

Well there's a pretty good reason for that, and it's not really the size, I don't consider that large at all. The reason you don't really see systems like what your planing is because like I mentioned, different plants have various different need. And trying to combine various different plants into one system, tends to yield poor overall results in comparison to using separate systems. So that's just not the route most people take. I know you have your hart set on creating a one system for everything setup, that's fine and I wish you luck if that's what you want to do. I would just suggest to be prepared for a "lot" of trial and error, as well as on the fly problem solving with such a system. Especially if you don't have experience growing things hydroponically yet.

ive seen drilled PVC used for large scale aeration before, works quite well...

Yes for large scale PVC works (provided you have enough holes, and their small enough), although I still like the soaker hose idea because it dosen't cost much (if any) more than PVC tubing. But large scale operations have some very important factors that set it apart. First is the very large volume of water compared to plant size and root mass. This is a very important distinction, because if not the plants would use up the dissolved oxygen faster than the air bubbles can replace it. Second is water circulation, commercial operations have water pumps that circulate the water in water culture systems. And lastly commercial operations don't use aquarium pumps, they use air compressors to be able to get the large volume of air required for such a system, as well as the higher PSI to create small bubbles through precisely sizes and spaced tiny holes in the PVC tubing.

P.S.
I would also guess they also employ another method of oxygenating water as well. I believe it is called an "air lift." That combines air bubbles to lift water in a tube, and allows it to overflow creating falling water that also oxygenates the water. It's used especially in large volume fish tanks. That is fish tanks that hold thousands of gallons of water. Here is a link to a thread where it was briefly discussed. There are a few pictures that basically show how it works. You can always build a smaller scale one. Basically it churns the air bubbles and water as the water rises to the top of the tube, before it falls back down, churning some more.

http://www.hydroponicsonline.com/for....html#post3666