If you are referring to the system in the other thread that uses the cement mixing trays as the reservoir in a water culture system. I believe the tops are made from Styrofoam sheets. It comes in 1/2 inch, 3/4 inch, 1 inch, 2 inch, and sometimes even 3 or 4 inch thick. If you can find it, the blue Styrofoam is even denser and more rigged. You can find Styrofoam sheets in the home insulation department of most home improvement stores. However a top like that can be made of anything. As long as it's flat, waterproof, you can make holes in it for the baskets, and rigged enough to support your plants weight when you lift it.

Thanks for the reply. I looked at the foam sheets and thought that they would not hold up well. I will visit Home Depot today and roam the store looking for something I can adapt.
This will be a Ebb-flow system.

Joe

I used plywood painted with Kilz. Works real well, but cutting all the holes wasn't very fun.

Is the Kilz a brand of the white waterproof roof insulation you paint on called "elastomeric roof coating"?

Like this brand:
Elastomeric Roof Coatings

I've never even heard of such a product, neat. It is actually just a primer and sealer.

Kilz

I used a dense foam used for insulating walls. I came in a 4'x8' sheet and is 1/2" thick. I worked perfectly so far. It was hard to cut with a razor. I will post a picture once i get it all together. i have my holding tank in the ground with 15 gallons of city water, and a big air stone running. I did not put any nutrients in the water yet. Today I canceled the 20-20-20 order and picked up some three part Flora system from a local Hydroponics dealer. I also got 16 plants of various salad plants in Rockwool setup today. I have a load of plants started at various stages, so I son't know if I will put any of my pepper plants in the Hydro setup yet. I'm a little concerned about PH, but I have so many plants going on city water, I don't know how important it will be to my Hydro setup. Comments welcome. Joe

I find the easiest way to cut Styrofoam is with heat. I use a small straight soldering iron. The cheep hand held ones you can get at radio shack for a couple of buck's, and have replaceable tips. I think I've read a little about that 20-20-20 fertilizer, but at this point I'm not sure if it was the same brand or not(because I don't remember what the brand was for sure). But I think it was a wise decision to go with a true hydroponic nutrient to start with.

pH is very important, check it daily. At least in the beginning until you get familiar with fluctuations. And get the pH drops instead of a pH meter. The drops are much cheaper, don't require calibration, wont give false results, and one bottle will last you a long time. The drops are also plenty accurate. Salespeople often try to sell you a expensive meter instead of the drops, on the basis that the meter is more accurate. But you just don't need to measure down to 1 tenth of a point. You just need to measure a range like 5.5 to 6.5, and not an exact number.

Wow, that was great of you to give such great details. I know from reading, and reading, and reading, that you have a lot of experience.
One interesting thing I just picked up off the bottles of PH control from General Hydroponics was that Rockwool will alter your PH as it breaks down. The instructions say to avoid Rockwool, and construction grade aggregate (pea gravel and shale, they can dissolve slowly and cause PH to rise or fall. How much of a problem is that? Everybody and their brother is using Rockwool. I even got some RW plugs to start a bunch of salad greens for my Hydro system.
Ok, when you say PH drops, can you give me a company name that makes them?
I already realized one mistake, using city water to water my plants. I will switch to my well, which from my pond days, I know to be a very good and very easy to adjust. It may not even need adjusting. That blurb about Rockwool has me getting a little confused, if you can't go by what thousands of others are doing with great success, what can you go by? Thanks for the great help. I hope to be running by the weekend. Joe

The pH drops I use are from General Hydroponics. Just about any hydroponics shop carry's them, and usually run anywhere from $6 to $8. The directions say to fill the vial half way with the water, then add 3 to 5 drops. But I now only fill the vial about half a centimeter (or about 1/3 the recommended half way), then only use one drop. Depending on how often I need to check pH and how many systems I have going, one bottle of pH drops generally lasts me six months to a year.

You just match the color the water turns, to the color on the graduated color chart on the back of the bottle. And again, unlike what some sales people may tell people, it's very easy to read the color. Generally you'll always want to see a bright yellow (6.0), which is right in the middle of the pH range for most plants. If you want the pH higher, you'll want to see a green tint to the yellow, the darker green the higher the pH. If you want it lower, you'll want to see a orange tint, the darker the lower the pH.

General Hydroponics pH Test Kit

As for roockwook I personally don't use much of it. Mostly for a few reasons. One, it's expensive in the amounts I would need. Two, it's not easily conformable to most of the containers I use (like 2 and 5 gallon buckets). Lastly, it gets waterlogged easily if you don't carefully control water flows. But if using large amounts of rockwool as a growing medium, it's probably best to fallow their directions and pH adjust it first (by soaking it in pH adjusted water).

The only thing I use roockwool for is starting seedlings in the one inch cubes. Then I transfer the one inch cubes into the other growing medium (usually coco chips) in the hydroponic system. I have never pH adjusted the roockwool cubes before I use them myself, and with such small amounts being introduced into the systems, and I haven't seen any pH problems. Probably because I use such small amounts of roockwool growing medium.

I have never herd of pH issues using pea gravel, but it's a common growing medium. I cant say I have exactly used it myself, but I do often use rock that I get from our back yard. Our ground is more rock than soil here in the desert, and I can take a rake and scoop up a 5 gallon bucket full of small rocks in about 5 min. I rinse it real well with the hose on the driveway, then soak it in bleach water to sanitize it (kill soil born pathogens, and fungi). Then wash off the bleach water before using it. I haven't had any pH problems myself. Though I don't doubt some type of rock may affect pH, especially limestone. But river rock, pea gravel, lava rock, fish tank gravel all have been used in hydroponics. I have even used silica sand, however I did have a pH issue with that. But I never determined if it was due to the type of sand I used or not. Sand is also a common hydroponic growing medium, in fact sand is a primary growing medium used at Epcot center in Florida.

Well water can pose it's own problems also (unless it has a good filtration system, including UV light). Well water can have unwanted minerals in it, and it may contain soil born diseases and pathogens too.