from my experience it doesnt wick at all.

It doesn't exactly wick, and yet it "conducts", holds and disperses some humidity.

hiddenleaf, I guess you should explain how and exactly in what way you want to use expanded clay in NFT - and also specify "passive system". Only then people can tell if it is the right choice and if it will work or not with that technique.

Thank you Chinamon.

Lucas Formulas. Well for now I have an undersized pump, and I wanna do a flood and drain, but again, the pump is too small. On the other hand I believe it provides enough of a flow for an NFT. I do suppose that it would be good for plants that have a root system to take advantage of the tiny flow of water, but I wanna start seedlings in the bed. I guess it was just good thinking. I could have that set up by the end of the day if it could work. I was wondering if it can be done, but Chinamon is probably right.

Are you sure your pump is undersized for a a flood and drain and sufficient for an NFT instead. I've been using a tiny 4.5 watt pump with a head (vertical lift in height ) of only 45 cm for some E/F or F/D systems.

The important thing is that the so called head is sufficient to lift water as high as the difference between reservoir level and outlet. And that can be altered, respectively minimized. Raise the reservoir, and your pump reaches higher. Don't put the pump at the bottom of the reservoir but in the middle and you win another 10 or 15 cm or 4-6".

A conventional E/F or F/D system needs no pressure, - if the growing area is only filling slowly but surely and to the wanted level, that's not an issue.

As for an NFT system, the media you use in the net pots is not the point, some people use in fact expanded clay for that purpose. The point is to have your roots growing out of the media, the way they reach and dangle in the flow of the channel. With some NFT channel designs the distance between net pot bottom and channel floor is just 1/4" or less, the way you can transplant as soon as the roots show up at the bottom of the net cup. If you are using some standard PVC tubes instead, this will not be the case (distance will be much more) and perhaps become an issue.

Don't put the pump at the bottom of the reservoir but in the middle and you win another 10 or 15 cm or 4-6".

The head is measured from the water surface height so you won`t gain any extra by placing it halfway up ;)

in my NFT runs, the bottoms of the pots are about 1/4" above the bottom of the trough. to keep things wet, I blocked the end of the trough about 1/2" high, so there a depth of water in the trough deeper than 1/4". as soon as the roots start coming out of the pots, you simply pull off the end blocks and it goes back to straight NFT.

>>The head is measured from the water surface height so you won`t gain any extra by placing it halfway up ;)Is it "measured" or is it calculated from the water surface? I am concerned about the real head, not the one who is given (measured) by the manufacturer, as it never corresponds and is of no interest here. The physics behind that make me real curious now. If the head would be calculated from the surface as actual and constant (as in a role of physics), I would have the same head measured from the surface of a well, weather I just dip a 4.5 watt pump a few inches deep in the water or if I let it down a 100 ft (at the end of a 100 ft long hose of course). You tell me... and tomorrow I'll test that by letting a small pump down a 4" and about 2m long water pipe and see if the actual and measured head from the surface remains constant. ;-)

Excluding frictional losses of the 100ft pipe.
If your pump is 4" deep you will have 4" column of water in the outlet pipe working against the pump.
You also have a 4" column of water working with the pump on the inlet side. 4"-4" = zero.
Hence the head is calculated from the water surface level.

So my pump is a Quiet One 200 made by Lifegard Aquatics.

http://www.lifegardaquatics.com/pdfs/q1200400DS.pdf

It pumps 53GPH at 1.64 feat of head (the head is where you attached the tubing right?) The pump pump was resting on the gravel. From gravel to top of aquarium 1' 3 &3/8" . Plus the depth of the grow bed at 6" is 1' 9 & 3/8". I didn't account for the tank dimensions. I want to use the gravel as a filter so the pump doesn't clog, so it has to be at bottom. You said 500 to a 1000 liters pump hu?

the head will be a hair over 1'-7.1/2"(1.625') so the distance from your lowest water point (remember the water level will decrease as the table fills) to the highest point you want your table to fill to (normally a hair higher than your overflow level)must be less than or equal to 1'-7.1/2"

If the height is less than that, it will fill faster. If(or when) it is exactly 1.64', it will push 53 gph.
Also, there are 7.5 gallons in one cubic foot, so you should be able to figure approximately how long it will take to flood the chamber.

My eyes glossed over a bit and I'm not following you at all. I've never noticed an increase in how quickly the pump filled as the water level in the tank dropped. On top of that, all the charts I've looked at from different brands say the same thing. The higher you have to move the water, the less g/lph. I'm not saying your wrong since the only experience I have is putting together an airlift pump and one experience with my recent project, I'm just not following you at all.

I forgot to mention that from the gravel to the top of the aquarium is less than 1.64' and the water level was much less than that. Maybe about a foot. I had a 3' tube attatched but that was coiled and level so the pump didn't have to deal with any extra height. Maybe that effected the flow rate, but I doubt it did by much.

>I've never noticed an increase in how quickly the pump filled as the water level in the tank dropped.Grizzman`s advice is on the money. When the reservoir water level drops by 6", the pump will have to lift the water the extra 6".

Why when the distance between the pump and the grow bed hasn't changed?

"The head is measured from the water surface height so you won`t gain any extra by placing it halfway up ;)"

Ahh that explains a few things, my little pump was struggling on one of my systems as the water level dropped, I thought it was some sort of water pressure when the reservoir was full that gave it more oomph.

Consider a pump (not switched on)in a bucket of water.
The water fills the pump and the outlet pipe level with the surface of the water in the bucket.
If you lifted the pump 6" higher in the bucket would you gain anything? nope, `cos the water in the pipe just dropped down 6" to match the water level in the bucket.
Head is measured from the surface of the water ;)

gravity and friction need to be calculated in the head pressure capacity as well.

Hey hiddenleaf, you could get a flood and drain fitting, mount it to the bottom of your grow bed and save the 6 inches of grow bed height? The overflow drain fitting with extension will start draining at 5".

{{gwi:1000412}}

Just looked at the pump specification.
53gph is the maximum open flow, 1.64ft is the maximum height the pump can lift water with zero flow.
To get any flow you will need to keep the vertical height from the water surface in the res to the fill height of the growbed to less than 1.64ft

what does that have to do with the flow of water when the pump is switched on? I want to understand, but I feel dense right now. What diff does it make if reservoir is 6" deep or 6' with the pumps ability to move water?

The total lift height is water height plus the pumps max head.
Every inch of water you pump from your res will cost you an inch of head. If your res drops by 1.64ft the pump wont have enough head capacity to push water any higher than the top of the res.

I think what hex is saying is this. Think about your pump sitting at the bottom of you reservoir, with the hose connected going up to the grow bed. Now, in the hose there will be the same level of water that is in the reservoir. That's where the air will begin in your hose. So, from that point, that's where you will start from measuring your head.

Are you saying that in like an airlift pump, the amount of water pressure has a direct influence on the pumps ability to move water?

Read the pump curve below and see how centrifugal pressure and flow are related. Follow any constant RPM line.

Why bother with theory and physics at all here?
If you have sufficient head and flow, you fine. If your head/flow isn't sufficient for the setup you plan, reduce the distance between reservoir (it's water level) and the outlet of the tube. To lift your reservoir from ground, a couple of bricks and a panel will do. That's it. You may also chose a barrel shaped reservoir to reduce the actual difference in level. If the pump is simply undersized for the purpose, save it for a later use and buy the next stronger model.

I appreciate all the technical training, but I'm not yet ready for a full scale commercial operation. I'll just have to figure out what my next move will be. I can't move the pump any closer to the grow bed so I'll use it in a DWC I've been wanting to throw together.

So did I guess right about water pressure?

Look hiddenleaf, how much is the next stronger pump that WILL be powerful enough (if the other was just coming a little short) for the setup you initially wanted to build? why not buying it?

Will you change your mind several times until the setup you'll finally build will fit the small pump you have got? Or will you buy the pump that is needed to realize your actual idea...?

Its better to have a pump thats too strong than one thats too weak, you can always divert some of the extra flow back to the res to add aeration. Something like this would fit the bill for most hydro setups. Maxi-Jet 1200, 20 W, 295 gph, 69" pumping height..$27 or less.

http://www.aquatic-eco.com/subcategories/122/Maxi-Jet-Powerheads

Well the expanded clay I ordered will float for ever more. I put a few into a cup of water and it has been floating for several days now. I think the ebay seller ripped me off, but oh well. So I guess F/D is out of the question, but I can fill the grow bed with enough water that the clay doesn't float and insert a drain pipe there. I could add an air stone in the grow bed for extra aeration and see if the set up will cycle with out adding any kind of extra filtration for the aquaponic system....or should I just go with a recirculating DWC in a 5 gal? Oh the painful choices :)

I think I've spent enough money lately. I think I'm gonna see if I can get close to what I want (for now) with what I have on hand. Thanks for the help and the link hex and lucas