If you search this forum (on the main hydro page near the bottom) there was once a discussion / thread where someone posted exactly how much water a lettuce plant consumed in its life cycle. That thread would probably be of great interest to you.
I've seen youtube videos of commercial hydro lettuce setups and they seemed to used full size sheets (4'X 8'). I would wager the plants were spaced at 6"-8" apart. make you "pools" about 1/2" wider than the long raft dimension (thus 8'-0.1/2") and 1/2" per sheet than the narrow dimension. so if you wanted 3 rafts in a single pool the dimension in the other direction would be like 12'-1.1/2". of course, 1/2" might be too much but you want to make sure the rafts can rise and drop freely.
If you're going to have more than one pool, you could have them all piped to a central reservoir where the nutrient is adjusted and aerated, but I believe in that other thread it was said they simply float the rafts until harvest without any kind of aeration.
Anyway, I hope that helps a bit. feel free to ask if you have any more questions.

Don't use air pumps. Water pumps work much better to aerate. Spray the pump output back down against the top of the water.

Just look at the recommended spacing for the variety of lettuce you want to grow. I'd guess you would need about one square foot per plant, but you have to experiment and see what works best. Only the miniature lettuce heads can be grown at six inch spacing.

Deep water culture works the best in warm climates, compared to other methods, because the large body of water keeps the roots at a constant temperature. There is no one dimension of tank that is correct; everyone's seems to be different.

Thank you for your quick answers and advice!

I will search for that exact post.

That is precisely why I want to use this system, because of the tropical climate over here. I live 800 Meters above sea level so it gets chilly at night. Overall I believe that the temperature will be not a problem.

Water pumps work best to aerate, got it.

Thanks a lot grizzman and Cole_Robbie, you have been very helpful. I am designing the layout right now, and if more questions arise, I'll be back.

Cheers.

Just 1 more question..

Would it be safe to say then that the Water Pump will work if I install it inside the Reservoir? And not inside the tank(s)?

I think I'm a bit confused with the -Water Pump and Air Pump/Air Stone- equipment. Will the water pump replace the Air Stone and Air Pump?

I saw this image, and I had the idea that the tank had to be aerated. It tends to get a bit confusing.. I know that trial and error (experience) will work wonders, but I just want to make the minimal amount of "mistakes" from the start.

Thanks again.

You may want to consider aquaponics. Lettuce doesn't need a high concentration of nutrients, and fish like talapia can be used, cutting your costs way down, and also providing another 'crop' to market

A couple of years ago I saw several videos on youtube on growing lettuce commercially. One video that really caught my interest was of a commercial system in Mexico. The video showed the whole process from seeding to harvest and was very interesting.

The fish people are your friend. Look into the ways that fish farmers aerate their ponds. Aeration comes from surface agitation. You can do that with air or water. I personally prefer using water. Pump it into a manifold over the tank and spray it downward. You don't need misters, just holes in the manifold. If you move enough water with a big enough pump, your system will stay very aerated. Your pump is too big when it starts to heat the reservoir. Until then, the plants will love it.

@RoboGeek

I have seen that method before, I will look into it, thanks.

@ fintuckyfarms

I'm going to look for that video too. Thanks a lot.

The picture is just a rough representation of what the final design would be (reservoir and water pipes missing). I want to start my experiment with 120 or 240 plants (1 or 2 tanks). I can access the plants by lifting that structure since it will be very light (but anchored to the floor by hooks). For now, I think this will be the best method for me. Oh, and the 2 ends have a type of Screen that allows air circulation.

This week I will look for a solution for those Tanks. I want them to be made of some kind of durable plastic. That is my biggest concern I guess.

I read on the forums that I can use a Soak Hose for the air bubbles. That does not sound too complicated. Just let the hose run on the tank bed all the way across the other end.

I will find a quote for the PVC pipes and the plastic cover tomorrow.

Thanks for everything, and lets see how this experiment turns out ;)

And here is the pic..

@ Cole Robbie

Thanks for the tip ;)

What is the cover material made of? Is it shade cloth? That's fine, but it comes in different kinds that allow in different levels of light. You will have to find the one that suits your weather, and you may have to change it at different times of the year. If you attach it with wiggle wire, you can take the cover off and on easily.

The cheapest way to build your tank is to simply make a wooden frame and put a pond liner in it. I'd use 2x12 or 2x10 treated lumber. Put 2 metal brackets on each corner to reinforce it. Obviously, keep any sharp edges off the pond liner. My own design for a lid uses a very common white fiberglass paneling that comes in 4x8 sheets. Sandwich a layer of styrofoam between two pieces of that paneling, hold it together with galvanized bolts and washers, and seal the edges with clear silicon. The lid is the most expensive part, but it lasts forever, and your tank will cost very little compared to buying a pre-formed plastic tank. You can get by with just styrofoam as a lid, but it will wear out much more quickly.

Hi Cole.

I got the idea from this picture I saw in Google. I have to ask around if they sell any 'greenhouse-designed' covers just like that one.

Thank you for the tank idea, I will look into it ;)