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water DWC in conical reservoir - super easy water changes

Uncle Eckley

Extreme Member
Readying one of my DWC reservoirs for a new plant today and had everything all clean and pretty, so thought I'd show and tell.  I run a little 36x20x63" grow tent in the closet next to my chair and I need things streamlined to make up for the narrow access I've got to the tent.  (The doors slide one behind the other, so can only open one side at a time.)   
 
The biggest problem was water changes.  Next to my chair, I'd done hydro in 5-gallon buckets.  Changing the nute solution involved lifting the lid of the bucket plant and all off the working reservoir, setting the plant on an empty standby bucket while I worked, then schlepping water in to mix and pour into the working reservoir before returning the plant to its place under the light.  This was a pain and disturbed the plant being changed and usually all of its neighbors, too, especially as the plants grew larger. 
 
The first thing I tried was beverage dispensers with a spigot.  They actually worked well.  I set a wire shelf that spanned the tent parallel to the floor at about four inches up and set the beverage dispenser reservoirs on that.  This let me slide my long, flat waste receptacle under the shelf so I could simply open the spigots to drain away the old solution.  The only problem was the beverage dispensers wouldn't drain completely.  There'd be a half-inch or more fluid left in the bottom unless I picked them up and tilted them around, which of course partially defeated the purpose of having the spigots.  I needed something better.
 
The waste receptacle was an important find.  It's meant to catch used oil when changing the filter on a motorcycle and holds around three gallons of fluid, which is almost enough, lol, will get to that later.  Anyway, it was a little expensive, but the thing was just perfect for my application; the broad side intended to catch the oil is faceted to a shallow concavity with an inlet at the center to make a funnel of the entire container (pictured below).
 
I realized I needed a container with a conical shape to the bottom if it was ever going to drain completely without fussing with it.  There are loads of tanks and hoppers and scientific glassware available with such a shape, but much of it is prohibitively expensive for what I'm doing.  I figure it's one of those bloated captive market things - nobody's paying for this stuff out of pocket, it's always a business expense to write off, so why not get rich and stick it to the taxpayer?  Anyway, after much searching I found just the thing - on Amazon, of course, lol!  This is a conical fermenter.  I gather folks ferment stuff in it.  I've never messed with that but..  This. Thing.  Is.  Perfect.  I get 2.5 gallons of fluid in there comfortably, it's got a big ass ball valve (comes apart for cleaning - awesome) with a barb fitting at the bottom, a screw on cap that's already got a small hole in it (for the airlock, but I stick a grommet in there and run the air line through it), AND it comes with a wire stand that looks taller than it should be, but is actually just right.  They're more expensive than the iced tea tanks, but they're worth every penny. 
 
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The plant never has to move.  I lay my motorcycle oil pan receptacle (black at left there) on the floor in front of the tent, attach a PVC keg hose to the barb fitting on the reservoir valve, and run it into the inlet on the waste tank.  Then open the valve and wait for the reservoir to drain.  Once it's drained I run a gallon or so of fresh water through to rinse, then close the valve and the waste tank and set to refilling with fresh nutes.  I pour the used waste fluid over my roses out front.
 
Three-inch hole saw to accept a net cup.  I used to wrap the foil first then press in the air line grommet, but I'm too lazy now to make it look pretty.  Would have done if I'd planned to take these photos.  The air line is connected with a few elbows to help keep it from swimming around in the reservoir.
 
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There are a few suction cups in there too that seem to work.  I thought for sure they'd let go, but nope, they hold.  This is all to try to keep the roots from wrapping around the air line and upsetting the air stone whenever I lift the plants for inspection of their nethers.  Forgot to have one of the orange rings for the air stone printed for this one.  Sorry for the crappy shot, was juggling everything.
 
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This is my third- or fourth-generation net cup, can't remember.  Long arms with plenty of holes for low stress training ties.  The cubicle space fits a 1.5" Grodan cube and lets me use very little Hydroton.  Some plants do without any at all on top, just a few pieces in the pyramid at the bottom to help wick up nutes early on.  
 
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Bucket with a Uniseal, ball valve, and barb fitting makes mixing and refilling a breeze!
 
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I'll never grow DWC in a bucket again, this is too much better all around.  (Well, except for the cost, which isn't too bad.)  
 
As always, any and all questions, comments, and criticisms are very welcome and I thank you all most warmly for reading my noodlings!    ;)
 

Uncle Eckley

Extreme Member
Had to fish out the suction cups on the air line from inside the newly swapped reservoir. They had come loose and one had settled in the neck and clogged the valve. :^\
 

Siv

Extreme Member
E, I think you would be better off with just a large heavy simple airstone - those disky ones seem to be more trouble than they're worth. I have problems with the strip type which are plastic on the bottom in my reservoirs - they just kept flipping over.
 
E, I think you would be better off with just a large heavy simple airstone - those disky ones seem to be more trouble than they're worth. I have problems with the strip type which are plastic on the bottom in my reservoirs - they just kept flipping over.
Believe it or not, you get as good/better oxygenation with just simple surface agitation. If you don't mind noise, you can waterfall the return nutrient.

The problem with airstones, is that the water column in 100% of reservoirs isn't tall enough for oxygen to completely dissolve into the liquid, on the way up. So no matter how fine you make your bubbles, you're just making bubbles. Most of the oxygenation occurs at the layer where air meets water.
 
I should have added, that most of the time when I use an airstone, it's to act as a "muffler" to quiet down the noise. I don't really value them much more than that. They become a maintenance item, as the gunk up, and need to be cleaned or replaced.
 

PaulG

Extreme Member
Super awesome set-up, Unc!

It has been great fun watching your
experimentation over the last few seasons!

Keep up the good work!
 

Uncle Eckley

Extreme Member
Believe it or not, you get as good/better oxygenation with just simple surface agitation. If you don't mind noise, you can waterfall the return nutrient.

The problem with airstones, is that the water column in 100% of reservoirs isn't tall enough for oxygen to completely dissolve into the liquid, on the way up. So no matter how fine you make your bubbles, you're just making bubbles. Most of the oxygenation occurs at the layer where air meets water.

I've read this before. How tall would the reservoir need to be? I'm guessing pretty damned tall..

What would happen if I were to completely overdo the aeration (or goof around trying)? Just charge the hell out of the solution with air until you had a churning froth more than a bubbling column?

Super awesome set-up, Unc!

It has been great fun watching your
experimentation over the last few seasons!

Keep up the good work!

Thanks, Paul! These have been working great. The only problem is the plants grow so big and tall I can't move the light up high enough in my little tent. I had to take out the giant carbon filter the other day to make room to raise the light again. I exhaust up into the attic; not sure what the carbon filter's really doing for me, anyway..
 
I've read this before. How tall would the reservoir need to be? I'm guessing pretty damned tall..

What would happen if I were to completely overdo the aeration (or goof around trying)? Just charge the hell out of the solution with air until you had a churning froth more than a bubbling column?

If you were to try to just overkill the aeration, you'd end up with more surface agitation, which still plays to the original premise...To be honest, I'm not exactly sure how much head you'd need to completely dissolve bubbles... But you'd know, because they wouldn't make it to the surface. The basic idea, is that you reduce the bubble size, until the pressure of the water column, forces the air out of the bubble - thereby causing it to collapse - and forces the oxygen into the ambient liquid. It's not straightforward, though, because it's a function with multiple variables. Pressure (head), bubble size, temperature, and probably something else that I'm forgetting. And of course, it can't be stated enough, that the ability of any liquid to absorb oxygen, is temperature based. So there is a point at which you can pump in all the oxygen you like, and it won't be of any benefit at all...

NFT hydroponics works so well, because there is a constant, uninterrupted water/oxygen interface. Think of it like this.... If you aerate, you have the surface area of a bubble sliding through the surrounding liquid - which is your interface area, and potential oxygen exchange. In NFT, you have the surface area of water, in whatever the size your channel is, making constant contact with air. Provided all the other variables are in check, you have far more potential for total dissolved oxygen in that scenario, vs pushing a bubble through a water column. Smaller bubbles equal more total surface area, but still pale in comparison to the waterfall effect.
 

Uncle Eckley

Extreme Member
If you were to try to just overkill the aeration, you'd end up with more surface agitation, which still plays to the original premise...To be honest, I'm not exactly sure how much head you'd need to completely dissolve bubbles... But you'd know, because they wouldn't make it to the surface. The basic idea, is that you reduce the bubble size, until the pressure of the water column, forces the air out of the bubble - thereby causing it to collapse - and forces the oxygen into the ambient liquid. It's not straightforward, though, because it's a function with multiple variables. Pressure (head), bubble size, temperature, and probably something else that I'm forgetting. And of course, it can't be stated enough, that the ability of any liquid to absorb oxygen, is temperature based. So there is a point at which you can pump in all the oxygen you like, and it won't be of any benefit at all...

NFT hydroponics works so well, because there is a constant, uninterrupted water/oxygen interface. Think of it like this.... If you aerate, you have the surface area of a bubble sliding through the surrounding liquid - which is your interface area, and potential oxygen exchange. In NFT, you have the surface area of water, in whatever the size your channel is, making constant contact with air. Provided all the other variables are in check, you have far more potential for total dissolved oxygen in that scenario, vs pushing a bubble through a water column. Smaller bubbles equal more total surface area, but still pale in comparison to the waterfall effect.

Makes sense. So DWC is kinda bullshit. At least in the purported effect. So what's actually happening when I stick an airstone in one of these reservoirs? It's clearly more effective than "Kratky"-style with no aeration. It's oxygenating, just nowhere near as well as hoped/believed/intended, and nowhere near as well as surface agitation?

Now I'm thinking paddle wheels.. Whisks..
 
Nah, DWC isn't bullshit. It's just that there is a mistaken belief that more fizzy is necessarily better. The bubbles in the water aren't really what's doing the heavy hitting. It's the movement they create at the water surface (well, some small amount of oxygen will be dissolved, but it's not the main constituent). I have proven this several times over. First time, I had a home built system, that was nothing more than a tote with holes cut for root baskets. I started out with the best airstones I could find - which happened to be wood. I pumped mega air through them, and produced a solution that was so bubbly, it almost wouldn't permit buoyancy. But one day, the stone was clogged. So I removed it. I'm lazy, and didn't change it for months. And I literally had no negative effect from a lack of diffuse air. (you'll know if your system is working, because there will be a constant layer of condensate in the root zone - and of course, the plants will show you)

Truth: if you maintain a good airspace at the rootzone, and you have something - literally ANYTHING - that causes the solution to move, you are going to do just fine, provided all other parameters are in check. However, I think you may find that the RDWC systems are a bit more effective, and don't rely on the use of an airstone.

Please keep in mind that I'm not trying to slag your setup, at all. I just wanted to share that I appreciated the reduction in complexity, when I realized that the air pump and stones weren't really required. And while I wouldn't tell you to scrap what you have - because it WILL work - just maybe think of trying the RDWC, if and when you decide to scale up. I think you'll be very happy with it.

Heck, you could even RDWC your existing device, by hooking the pump at the bottom of your conic, and then pumping the return solution back to the top. You could even angle the return line, so the solution follows the contour of the container when it's pumped back in. The more surface area it covers before returning to the reservoir, the more oxygen interchange. Water changes still a snap. :)
 
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Uncle Eckley

Extreme Member
Please keep in mind that I'm not trying to slag your setup, at all.

Dood. No way. I'm soaking this up.

Heck, you could even RDWC your existing device, by hooking the pump at the bottom of your conic, and then pumping the return solution back to the top. You could even angle the return line, so the solution follows the contour of the container when it's pumped back in. The more surface area it covers before returning to the reservoir, the more oxygen interchange. Water changes still a snap. :)

I really like this idea! The fluid action would be nearly silent, like pissing against the back of a urinal, lol. I bet I could coat almost the entire surface of the air volume with only three or four spouts.. I've got a nice NIB Eheim pump that would easily drive both bulbs, but I stagger sowings, so I can't use a master reservoir.. Oooh! Or what about droplets? How long do you think before I'd have to descale misting nozzles? Could drive those with smaller pumps..

Going to hijack my own thread a bit here, but I've got a pH question for you, too. I'd been having calcium problems in the latter half of my plants' lives - nothing show-stopping, but unsightly and no doubt detrimental to some degree. I know there's plenty of calcium in my solution, so I raised my pH target to 6.2 which all but completely cleared it up and now I'm humming along. So why do so many folks maintain 5.8, 5.9?
 
The 5.8 and 5.9 are most likely the "theoretical optimal" - but as I stated before, "optimal" is temperature based, and pH plays right into that. You'd want your reservoir temperature at something like 68 degrees, at all times. Uptake is definitely a function of both pH and temp, so that would be my best guess. Although, in truth, I'd not really try to hold 5.8 or 5.9, and if I saw calcium build-up, I'd sooner scale back on calcium input. However, I'm also VERY conservative when it comes to nutes. I don't like to go heavy. I like to use the absolute minimum that I can get away with.

With regards to your container and RDWC... There are commercial variants of nutrient hoppers that actually incorporate a pump at the bottom of a very similarly shaped (but much larger container, that return the nutrient solution to the top of the tank via a 4-way splitter. It's very quiet/ In fact, a local place here has one of these setups, and they use it to brew AACT. So, if that's any measure of how much aeration you get from RWDC, considering how much emphasis is placed on aeration in a compost tea brewer...

I'm trying to find out what the name of that beast is. I'll call the place in a bit. When I find out, I'll post a reference. I think you'll be surprised to see how similar it is to a combination of what you've done, and what I'm describing...
 
So... the equivalent to what I'm describing, is called a "vortex brewer". Not going to be what you're after, because it' creates an open swirl in the middle of the hopper. It also uses an air pump, instead of a motor (we could discuss why an air pump might work better when you're building pressure and leveraging pressure differential into your system, but it's a different convo). But look at the design of them. I think a small pump, pushing water back into the reservoir, at an angle that maximizes surface contact with the wall of the container in the air space, would do well.

Here is the vortex brewer:

 

Uncle Eckley

Extreme Member
So... the equivalent to what I'm describing, is called a "vortex brewer". Not going to be what you're after, because it' creates an open swirl in the middle of the hopper. It also uses an air pump, instead of a motor (we could discuss why an air pump might work better when you're building pressure and leveraging pressure differential into your system, but it's a different convo). But look at the design of them. I think a small pump, pushing water back into the reservoir, at an angle that maximizes surface contact with the wall of the container in the air space, would do well.

Here is the vortex brewer:


Looks like they're squirting in toward the center to create the vortex whereas I'd want to squirt out against the walls. Looks like they're made of money, too, lol.

You've certainly got me thinking.. Thanks for the link!
 
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