Planning my setup, input needed

[GpsFrontier]

Do I need any special thermometer for it? I am not sure what the impact of the nutrient solution is on a "normal" thermometer.

No special thermometers needed. I use a fish tank thermometer myself, I got it at a local store (WalMart) for under $2 US dollars. A glass one, not the kind that stick to the side of the tank, I don't think those are accurate enough (especially over time). It does have a suction cup on it to stick it to the glass, but it's a regular glass thermometer. I don't leave it in all the time, it only takes about 5 min to get a good reading. I only check it when I have a concern. I just tied a string on it so I can drop it in and retrieve it easily. P.S. I store it in a empty plastic spice container to protect it from breaking.

About the bucket system: if I understand correct, in the lower bucket I place a piece of tube that will determain how much water will stay in the bottom acting as reservoir. However the top bucket will be above that level, so I assume I fill up the bottom bucket with hydroton pebbles so it reaches the top bucket? If not: please explain how the plant could wick up the solution.

Well there are really two ways to run it, either a flood and drain (ebb & flow) or a drip system. I am suggesting running it as a drip system, because it would be less complicated, and use a lot less nutrient solution than it would take to flood a flood and drain system. You are correct about the bottom bucket reserving nutrient solution at the level you decide. However running it as a drip system the pump feeds the growing medium from the top, making it's way down through the growing medium, and draining into the bottom bucket. The tube height in the bottom bucket is determined by the overflow tube. Once it overflows the tube it drains down into the PVC tubing that takes it back to the reservoir where (one pump) recycles it back. Each bucket will have it's own reserve, but all of the plants would be feed by one pump.

The size of the buckets, the placement of the bottom overflow tube are both key to the design. And are reliant on what materials you have to work with. Once the root system becomes large enough it will grow down into the bottom bucket where the reserve nutrient solution is. but if the top bucket is smaller than the top one, and there is enough space between both buckets, you can raise the overflow tube high enough so the reserve water level is soaking the bottom inch or two of the growing medium. This will wick up throughout the growing medium. It's all really about what you have to work with, and how you ultimately can design it. I can maybe do a quick image of what I mean tomorrow to give you a better idea. It is basically a DWC setup, but using much more growing medium to hold moisture. I don't see much difference between a dutch bucket system and a DWC system other than that. I believe a typical dutch bucket system is feed by a drip system, but like I said it can be run like a flood and drain also, just more complicated (fittings, running lines etc.).

How to determine the reservoir size? It seems to depend on the
Number of plants x
Bucket size x
Average uptake per day x
Ammount that keeps the pump from running dry

You are right here, all factors you need to consider, but I might add that as the plants get bigger they will suck up more water daily. Also they will suck up more as it becomes hotter. I don't have any magic formula (or even know where to find one). But as a comparison I was using a 18 gallon reservoir for my broccoli plants (by the way that is the bucket system in the earlier pictures, reservoir is under the table), I started out using just 8 gallons. But as the plants got bigger they were drinking much more water daily, I was replacing between 2-4 gallons a day. Many times it got to low and the pump was going dry, so I filled it to the full 18 gallons.

This gave me a buffer so I wasn't checking water level, and pH etc. twice a day. But as the water level fluctuates, so does the concentration of the nutrients in it (PPM/TDS), in the long run the bigger the reservoir the better. But also you don't want to waist nutrients either. This is part of the learning curve, and why I suggest starting small first so you can experience these things first hand.

[GpsFrontier]

I had time to make a few images of what I had in mind for the dutch bucket system. They are not done to scale, but I think they give you a better idea what I am/was thinking. Also the designs are drawn around using 5 gallon buckets for the large bucket, and 3 or 4 gallon buckets for the small bucket (that holds the plants). But the basic idea is what's important because I am not sure what you have available. You can use almost anything you can get your hands on. I can get many different size storage containers at the local Walmart fairly cheaply. You may even find local restaurants that are throwing away containers that would work for you.

Also to make it easy to draw, I made the overflow tube inside the large bucket straight, but you can use a flexible line if space is an issue. The key is the top of the overflow is above the bottom of the bucket that holds the plants. This way the growing medium will be able to wick up the water from the reserve in the bottom bucket, when/if power goes out. Problem is (as with the dutch bucket design) if the water level in the bottom bucket is too high, it can water log the root system (power or not). Getting the best fit for this level is the key to it working well. So you will need to do some trial and error with this height, as well as the type of growing medium you are using, and even time of year.

[sh4dowman]

Thanks for the great drawings! (what program did you use?)

This confirms my mental image of the system you described. I think it can be developed cost effective. Yeah I can imagine it needs some trial and error testing to see what will be the best water level to contain (based on the type of plant and weather conditions). That is why I intend to keep a logbook so I can always review things at a later time.

For the drip line: I have to see if I can find drip emmiters in here. Another option would be to use T connectors at the main line so each pot can have a punctured piece of tube that drips the water in it.

How about the pump? It seems I first have to design my system; then work out what ammount of water will be in it; and based on that (+ the distance to the pump) how much PSI it need.
I did follow this link: How to select a hydroponic pump

Can the strength be adjusted on the pump or do I need to make a valve between my dripline and the pump to control it that way? Not sure if that could have a bad effect on the pump.

[GpsFrontier]

Thanks for the great drawings! (what program did you use?)

I use Google Sketchup, they have paid versions but I use the free version at the bottom of the link. It takes time to learn how to use it. But from what I understand it works much like the CAD (drafting program, maybe even better). The CAD programs costs thousands of dollars. I have not used the CAD program so I cant compare. But Google also has videos that help give directions/instructions on how to use it best. I am no expert with using it, but I like it a lot. I needed a way to make the imiges for the pdf. files, and free designs for the build your own system plans for my website, in order to make them look somewhat uniformed. Google Sketchup fit the bill in my price range, FREE.

It is a 3D image program that you can rotate the images, then you need to export them from the program as a jpg, in order to use them like I have posted them. Once they are exported they are 2D images and not rotatable. But I save have all the originals (in stages along the way) in original form, so I don't need to start from scratch with every image. Although, I did start from scratch when creating the ones I posted in this thread, because I hadn't created any thing with that design yet. But it's not time wasted because I have no doubt that they will come in handy later.

For the drip line: I have to see if I can find drip emmiters in here. Another option would be to use T connectors at the main line so each pot can have a punctured piece of tube that drips the water in it.

To be honest, I think drip emitters are overrated. I don't know what's available to you, but emitters will clog. I use regular irrigation tubing (like the kind that they use for soil gardening). They sell (here) pre drilled holes, and solid tubing in all sizes. I just fit it all together the way I need it to fit, then take a paper clip (heat it red hot) and poke the holes where I need them. If they clog over time I will just poke more holes, but the tubing is much cheaper (to me) than replacing emitters.

How about the pump? It seems I first have to design my system; then work out what ammount of water will be in it; and based on that (+ the distance to the pump) how much PSI it need.

I don't know how many plants you plan, or how many. But the pump will need to be sufficient. Again I don't know what's available to you, but none of the pumps that I use are rated in PSI (pounds per square inch), but gallons per hour (GPH). Also the most important rating to me is the "head height," this is how many gallons the pump can pump at a particular height above the pump. This can drop dramatically depending on the pump. I attached a picture of my favorite pump so far, the head height is 8.7 feet. I actually needed to split the line in the reservoir because it pumped too much and the system would overflow (at 2 feet), one line went to the system, the other directly back into the resevar. But I got it for $45, and it pumps 3-4 times the volume that the pumps I got at the hydroponics store for $30 do. I got it at the local hardware store in the nursery department, where the sell fountain, and pond pumps. Just make sure it either has a filter built in or you create one, it needs a filter.

Can the strength be adjusted on the pump or do I need to make a valve between my dripline and the pump to control it that way? Not sure if that could have a bad effect on the pump.

Adjusting it would depend on the pump, the one i showed you has an adjustment, but the flow still needed to be adjusted down, for the application I was using it for. But I would rather need to do that than need to buy a new one if I needed a more powerful one. And yes, you you can place inline control valves to help direct the flow, especial if they are at different levels (heights). But I have not come across (or herd of) any problems of back pressure damaging the pump. Once you take one apart to clean it I'm sure you will understand why that is.