Adventures in hydro #3 - AAA or Air Atomized Aeroponics - for sure!

My HPA thread was getting way to long, so I decided to start a new one for my next experiment in hydro - Air Atomized Aeroponics, or AAA or AA depending on who you ask.

However, so far its not going to well, so this thread may be really short! :laughing:

I can on;y do this if its relatively cheap. I need to replace the main pump and some other small items if I want to continue with HPA. That was going to cost me somewhere around $150.

I can get an ultra quiet air compressor for about $120 on Amazon. Everything else I need I can scavenge from my HPA build - except for the air atomizing spray nozzles.

The very few people who have been doing AAA for the last several years have all banded together to keep the nozzles they use a super secrete. They refuse to tell anyone but the members of their group anything about which ones work and which ones dont. Well, the only thing that has been said is that you’re going to have to spend $100-$300 per nozzle. They are perfectly happy to brag about how great their grows are. They are also quick to tell anyone who asks everything they are doing WRONG - except which nozzles to buy that will actually work.

Im not going to say what I think about people like that, but its not flattering.

Anyway, thats waaaay outside my budget range. I have been casually looking for cheaper AA nozzles that might work. There are a bunch on ebay for $12 to $50 that look a lot like the $$$$ ones. Most all seem to come from China. You can get the same ones on Amazon, but for more $$. The advantage to Amazon is easy returns if the nozzle doesnt work and it gets to me in under a week instead of 3 to 6 weeks. So I ordered one for $22 from Amazon that sounded like it might be worth playing with.

I decided to try the fan shape first. I think I can get halfway decent coverage of the mist with two of these - one on each side of my chamber.

The other key aspect of this nozzle is its a siphon type - at least thats the claim. More on that later. That means it will siphon the nute water from a holding tank in the root chamber. The other options all involve pressurized nute tanks or a gravity feed. Siphon is what I want.

I had major issues on my HPA grow with controlling PH, and algae growth. The PH issue was at least partly due to my well water. When ever it get agitated, stirred, aerated, shaken, or just looked at too hard, the PH goes UP. A LOT!

So, I would really really dont want to have to pump nutes from my rez into a pressurized holding tank. The pumping and pressurization will surely cause me more PH headaches.

A siphon feed will be the least disturbing to the nute mixture between the time its forst mixed and when it gets sprayed onto the roots. It will also be the simplest, most reliable in all other respects and the cheapest way to go.

So I ordered one of those nozzles and hooked it up to my very very noisy shop compressor - and it doesnt work. It refuses to siphon no matter what I do. Instead of having suction at the water inlet port, it has pressure equal to the air pressure being fed to the nozzle. Any liquid will need to be pressurized or it will never spray.

Im pretty sure they sent me the ‘pressure’ version that requires the liquid be pressurized instead of the ‘siphon’ version. So, it is on the way back to Amazon. I should have the replacement in a few days and will see if that one works.

Fortunately, I have two or three months before it cools off enough so I can start my next grow. Lots of time to experiment.


Im giving up on the Amazon nozzles like the one linked above. I have been unable to talk to anyone who knows anything about the nozzles or any specs. As I mentioned before, I need a siphon type nozzle. When I asked the last person who emailed me back, they said all the nozzles were the same and all would work with pressure, or gravity, or siphon feed - which is 100% false. Either they have no clue or they are lying, so I give up on that.

I decided to try a differnt style of nozzle by a name brand company - Delavan. These are siphon feed type air atomizing nozzles used to burn fuel oil. Delivered price is in the same ball park - under $30.

There are two down sides to these, but Im sure I can get around both.

  1. They are normally installed into an adaptor that costs an additional $20 or so. Im going to fabricate my own. I should be able to do that from spare pulmbing parts I have on hand.

  2. These nozzles have a stainless insert for the actual orifice, but the rest of the nozzle is brass. They make a stainless version, but they run over $100 ea, so no go there.

Im actually not worried about the brass parts leaching copper into the nutes for a few reasons. First, Im going to be running this grow drain to waste, so the nutes will only touch the brass one time rather than re-circulating past the brass over and over. On top of that, the nutes will only be in contact with a very small area of brass, and only for a very short period of time - probably less than one minute. Plus, I will be running a lower than normal EC level, so there should be less leaching than in a normal hydro setup. Im hoping the amount of copper that does get into the nute droplets will help fight any algae - if that crap comes back, but I suspect the concentration will be too low to do anything at all. I have a copper test kit and will do some testing when I get the nozzle.

There are other sellers on ebay selling for a few dollars less, but shipping times are longer.

This particular version is rated to have a flow rate of 0.93 GPM at 5PSI with a siphon distance of 1". The flow rate and droplet size is controlled by varying the air pressure and siphon height.

The main positive reason Im going to try these, other than that I know it will work, and I can look up actual specs, is that they are designed to work with very low air pressure, and air volume. The other nozzles were listed as having a minimum air pressure of 40 PSI, so these Delavan 30609-8 nozzles will use far less air than the original ones I tried. That means a lot less compressor run time during the day and night.

With an air consumption rate of .87 CFM, that means a one second mist pulse will only use 0.0145 CFM per second. Im anticipating using two of these with an ON time of plus or minus 1 second to maybe 2 seconds or so.

That means 1 cubic foot of air at 5PSI will last some where between 18 - 35 minutes depending on my ON ime. My storage tank will be aprox 6 cu ft at 120 PSI, which is (very roughly) equal to 144 cubic ft at 5 PSI. That should mean the compressor will only run for a short time every 2400 to 4600 minutes or about once every 40-75 hours or so - if Im doing the math correctly.

That assumes I can set the cut-in pressure down to near 5 PSI, which I cant. So in reality the compressor will likely cycle every 20-30 hours or so or about once a day. I can live with that.

This is the compressor Im thinking of getting. I will be re-purposing my 5 gallon water accumulator tank as an extra air tank.


Here is a quick and dirty diagram of the basic layout for the AA setup. Its basically the same as my HPA grow with the changes needed. Its actually a less complex setup.

Costs are actually not that bad at all compared to doing HPA. The quiet compressors have come down a lot in price recently, which is a big help. The key cost variable is still the nozzles. If I can make the cheap options work, then the AA might even be less expensive to set up than HPA.

Quiet compressor = $110.00
Added 5 gallon air tank = $60
solenoid = $8
nozzles 2ea @ $30 = $60.

Oh crap - gotta run… more later…


You could try an ultrasonic fogger. They put out a nice mist basically. Mr Sparkle uses them to up his humidity and has some info about them in his journal here, they were really cheap.


Hi @beacher! Thanks for the suggestion. Lots of folks have tried those foggers, but with little success and lots of headaches.

Ultra sonic foggers generate droplets that are too small to work well for aeroponics. The fog they make is too “dry”. They typically generate droplets in the 5 micron size range. They also are difficult to keep clean and working well when you are using them with water that has nutes in it. The scale buildup - from the nutes - can ruin them fairly quickly.

NASA did some experiments in space several years ago and found that the ideal droplet size for optimum aero growth is more like 50 microns as an average size. Im hoping these AA nozzles I am trying will generate droplets between 20-80 microns, but we will have to see if I can get them dialed in to that general range.

To get an idea of why the 5 micron size droplet is considered “dry” when a 50 micron droplet is “wet”, you have to look at the relative volume of each droplet. The volume of a sphere increases as the cube of the change in diameter. A 50 micron drop is 10 times the diameter, which means it holds 10x10x10=1000 times as much water by volume. So each droplet in a 50 micron mist is 1000 times as much water as each droplet that is 5 microns in diameter.

Thats one of the main reasons droplet size is critical in aeroponics. There is also evaporation to consider.

Evaporation (in a constant environment) is a function of surface area. More surface area at a given temp and pressure means faster evaporation. You would think that a larger droplet would therefore evaporate faster than a smaller one - because it has more surface area. However, the surface area increases as the square of the diameter, while the volume increases as the cube.

That means that if you double the diameter of a droplet, the surface area goes up by 2x2=4 times as much. However, the total amount of water increases by 2x2x2=8 times as much. The net result is that very small droplets evaporate much faster than larger ones.

The evaporation of the droplets between the time they leave the nozzle and the time they hit the roots and get absorbed can make a very large difference in the EC levels you need to run in the rez. That evaporation is why HPA and AA aeroponics typically need a much lower average EC level than other forms of growing. Some aero guys are running EC levels as low as 1/4 of “normal” levels.

Imagine a droplet that starts at 50 microns, but evaporates down to half its size - 25 microns - by the time if finally gets absorbed into the root. That means the droplet will be .5x.5x.5=.125 times as big or 1/8th of its original volume. However, all of the nutes are still there in the droplet - but now its far more concentrated. The dissolved minerals stay in the droplet as the water evaporates.

That 1/2 size droplet now has 8 times its original EC level. So a droplet could start out at an EC of 1, but after evaporation, the EC is now 8.


Hi Larry,

Thank you very much for your reply to my questions about my setup. I’ll make all measurements and will return later.

As for AA nozzles in the first post, I am also thinking about them. But I’m going to order them from Aliexpress. From the primary source :joy:

It seems that there are only one producer and a lot of resellers. And some of the resellers have documentation with numbers. Take a look:

I read your thoughts about pressure tanks, but haven’t you thought that if we have lover pressure (like 2 or 3 bars) + small volume (for fast water changing), it may reduce all negative moments like PH, etc.


I think you find it useful :slight_smile:


Wow, it seems like you know your stuff. I just would have figured that smaller would be better, but I’m not about to argue with NASA lol. Thanks for the info!


Nice find on the nozzles and data sheets! I hope those guys know what they are talking about, and send you the correct ones. Keep in mind, I think you will want a narrow cone for your particular installation.

As far as a pressurized tank having problems, I think it will depend on your water and where you live. Many of my problems came directly from my water. Other people doing the same thing in other areas have not had the same problems I did. A smaller tank you can change out more often, would help though.

Unless there is a problem when I do the testing, Im going to stick with these Delavan siphon nozzles if possible. The Delavans will be a bit more difficult in some ways to fine tune. They dont have that needle valve built in for liquid flow rate adjustments. However, they will operate at much lower air pressures than the ones you linked to. Thats an important factor for me because I want the air compressor to cycle as little as often - due to noise mainly. Even that quiet air compressor I linked to above will sound very loud in the middle of the night - especially to my wife :slight_smile:


The Delavan nozzle arrived today, and Ive had time to do some preliminary trials. I think these will work great - if - I can get the air pressure under better control.

It never occurred to me it would be a problem, but I cant turn my regulator on the air compressor down to the 5 PSI range with any reliability. Its just not designed to work at that low a pressure I guess.

Whats happening is I get an initial burst of very hi pressure, then it drops down lower and holds for most of the cycle, but then it drops off at the end rather than a clean cutoff. This is with a 1 second ON time and maybe 4" of siphon height.

I am going to play with a flow restrictor/needle valve of some type, and different pressure settings and siphon heights. I also need to move the solenoid much closer to the nozzle.

When the air pressure is stable, the nozzle produces a very nice looking mist, but the initial burst and the slow taper down both produce large droplets. Its not much worse than the HPA nozzles, but I am hoping for a much cleaner, crisper ON cycle.

The only thing I could find at the local hardware store that fit the threaded portion of the nozzle even remotely was a 3/8" compression fitting nut. It turns out the thread is 9/16x24 UNEF thread. Not the kind of thing stocked in most hardware or plumbing supply houses around here.

So I went full McGiver and used some hot glue and a short piece of 1/2" PVC pipe, and a nylon flat washer to make the air connection. I have some 1/4" ID rubber hose that slips over the water inlet stub perfectly. Total cost zero - everything came out of my junk box :slight_smile:

I really wanted to make an air connection that could be threaded on and off. Plus I wanted a tighter fit for no leaks, but then I realized that I am only going to be running 5PSI or so into the nozzle, so no worries about blowing off the connection. I did several cycles at 50 PSI with no problems, so Im sure this will be more than strong enough.

By the way, at 50 PSI the mist is super fine - too fine Im sure.

So, now I need to play around with some sort of restrictor to see if I can get that to smooth out the air flow during the ON cycle. I suspect Im going to need a different regulator though - one designed to operate at much lower pressures than the one I have. Maybe an airbrush regulator? Im off to Google around…

Oh. some pics if anyone is interested.

This is the nozzle. The air enters between the stem and the threaded part. The water enters through the stem with the O-ring.


I managed a little more testing. Moving the air solenoid closer to the nozzle helped a lot with reducing the amount of sputtering and large drops. but the wildly varying air pressure was still not good. The only restrictor I could come up with in a hurry was putting a C-clamp on the air line tubing and squeezing it down. That worked kind of almost, but still not well. Plus is clunky, and imprecise, and it tends to fall off. The basic problem is my regulator is just not very good.

I ordered one of these to try out - 0-30 PSI range and with a gauge.

So far I have not tried to control the siphon height other than holding a small jar by hand. Im going to work on that aspect later today.

These Delavan nozzles will siphon at least a couple of feet, and it only takes the water maybe 0.1 to 0.2 seconds to get sucked up that far.


Today I had time to play with the siphon setup.

My original thought was that I would need to rig up a small tank that would sit just outside the root chamber that would hold nutes at the correct siphon height relative to the nozzles. That would be fairly easy, but I would need to fabricate or buy a float valve of some sort.

That would be fairly easy and not cost too much, but I wanted to see how well it worked with a gravity feed setup and a solenoid timed to match the nozzle ON/OFF cycle.

I like my rez sitting up on the work bench. Its easy to get to with no bending over, and having it raised makes it easy to drain. However, that means the water level in the rez would be anywhere from 12" to as much as 24" above the nozzle depending on where it ends up in the root chamber. These nozzles are siphon feed only - there is no check valve in the nozzle, so a gravity feed will make the water flow constantly - even when the nozzle is NOT soraying. That would waste a lot of nutes, big mess, etc. With a solenoid in-line, the water can only flow when the air is ON.

So I hooked every thing up and it didnt work for crap. Lots of run-on water dripping from the nozzle between ON cycles. After some head scratching I finally realized that solenoid must be leaking, so I swapped it out and now it works great! By partially shutting off a valve in the water line, I can control the flow rate from zero up to aprox 1 GPH. I have not done precise flow testing yet, but its in that ball park - which is in-line with the specs.

If it turns out I need to reduce the flow rate, I will need a better way to meter the water flow. Using a John Guest shut off valve is not precise at all, but with some fiddling I was able to reduce the flow rate by 2/3 to 3/4. Im hoping I wont need to do that, but I wont know for sure until the new regulator gets here and I have better air flow control - I hope!

With this temporary setup I was able to get a better idea of the mist quality, and droplet size. I’m not 100% sure, but I think its going to be very good. The mist seems to be more uniform than with the nozzles I used in the HPA setup. In other words, I think the droplet size falls in a narrower range. Fewer over size and under size droplets. The hang time appears to be excellent even with fans blowing in the room. I wont have good measurements until I finish re-doing the root chamber and get the nozzle mounted properly, seal up all the openings in the chamber, etc.

Plus I need to find my lazer toy. The kittens seem to have stolen it…

The new regulator will be here tomorrow, so more testing then…


Mission control - we are GO for launch!!

The regulator arrived and what a huge huge difference! I can easily turn it down to the 3 or 4 PSI range and it holds pressure well and the flow rate is very constant. The control know also allows for very fine adjustments. It takes several turns of the knob to go from 5 PSI to 10.

There is still a slight initial ‘burst’ when the solenoid opens, but I doubt that can be eliminated completely unless I spend big $$$ on the hardware. Larger diameter airlines would help, but all my fittings are already set for 1/4" tubing, so Im just going to live with that for now. This is going to work just fine for what I want to do. The mist quality is excellent as is the hang time.

The flow rate of the water seems to be fairly constant with different air pressures, but there is some variation. Interesting to me is that its not linear. The flow rate increases between 3 and maybe 6 or 7 PSI, but then it drops back down very slightly as you go above 7 PSI to 15 PSI. Looking at the mist as it sprays, it looks just the opposite. Higher pressures fill the chamber better. I am assuming that means the droplets are smaller with higher air pressures. Even though there is not a huge difference in the amount of water delivered, it looks like there is more mist at higher pressures. It has to be that there are more, smaller droplets.

The only potential issue I can see is noise. When the pressure is down in the 5 PSI range, the nozzle is fairly quiet. Maybe twice as loud as the HPA nozzles and not at an annoying frequency. Once things are all enclosed within the root chamber, Im sure I wont be bothered. The fans are noisier.

However, the amount of mist, as far as filling the root chamber, seems really marginal for a single nozzle or even two if I run at 5 PSI. Im going to need a minimum of two nozzles and probably three at 5 PSI.

I need to do a lot more testing and play with different nozzle locations before I can decide that.

I am tempted to use just a single nozzle and just turn up the pressure, or order a new one that has a higher flow rate, but there are potential issues with that.

The main one is uniform coverage. Filling the chamber with mist is a good goal as long as the chamber is fairly empty and the root mass is small. You can avoid spraying directly at the roots when there is lots of room. That allows the mist to swirl all around the chamber in theory. However, on my last grow the root ball got huge early in the grow. By the time I was 1/2 way through veg, there was no way to avoid spraying the roots directly. By the end of the run, the root ball pretty much filled all the space and there was no way to avoid direct spray. There was also no room for the mist to freely travel from one part of the chamber to another.

No matter where you put a single nozzle, some parts of the roots will get more spray than others. On my HPA grow, I ended up with a total of 5 nozzles - all with roughly 20% lower flow rates to these Delavan nozzles. One was under the main root mass shooting at the under side, three were on top shooting at the roots and one got swallowed on the back wall early on.

Based on the math alone, I would need 4ea of these Delavans to equal 5ea of the Ecologic nozzles. Im hoping I can get by with two of these Delavans running at maybe 7 or 8 PSI, because the mist travels and hangs much better and the atomization looks to be much more uniform with fewer over/under sized droplets.

All of that is going to need more testing though.

I have some videos of the mist. I’ll post one when I get it processed and posted to YouTube.

The next step is to UN-cludge my temporary setup. I have a rats nest of wires, tubes, solenoids, valves etc thats spread out all over my bench. Its very difficult to move around and adjust things. I need to clean things up and get stuff properly mounted and organized.

One of the things I need to determine is where to mount the nozzles. Im thinking near the bottom, shooting up for starters, but need to test that out.

Bottom line is - AA is a go and I am jazzed!!

Oh - just to let you all know, this is probably going to be another loooooong thread. I seem to be a compulsive detail poster :slight_smile:


This is a short video of 1 second ON time @ 5 PSI in the first part, but you cant see the spray. The nozzles is off to the side near the top of the chamber. Then I moved it to the top center, pointed straight down and upped the pressure to around 7 PSI in the second one. You cant really tell, but the cone angle of the spray get narrower as the air pressure goes up.


That looks pretty darn good.

Need to steal the laser back from the cats so we can see it better.


Dang… another thread to follow along and scratch my head about wtf is going on! Nice work sir


Thanks guys :slight_smile:

The kittens have hidden the light really well this time. I may have to get a new one. Their latest favorite thing is to climb the outside of my grow tent. Lots of little holes and tears! Rotten beasts!

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My root chamber from the last grow had too many roots stuck to it to make cleaning it worth messing with, so I made a new one. Its just two 30 gallon fabric pots hot glued together. I cut the bottom out of one and hot glue it on top of the second one. That makes a root chamber 24" in diameter x about 26" tall for a total of around 51 gallons or 6.8 cubic feet.

I am seriously considering abandoning one of the main tenants of HPA and AA aero - dont spray the root directly.

The main reason is its just not possible to do that for an entire grow unless you have a HUGE HUGE root chamber. Ive read every AA and HPA thread I can find, and of the few root chamber pictures that have been posted, not one single one showed a chamber large enough to avoid spraying the roots directly to one degree or another. This is especially true later in the grow.

One of the hallmarks of a successful aero grow is a huge root ball. The other one is that the roots will grow sideways and up - totally unsupported - out into space trying to reach the source of the water. My HPA root ball grew sideways faster than it grew down and roots climbed vertically in open space until they reached the top of the chamber.

My initial testing looks like I can go down to 0.2 seconds of ON time with these nozzles and still have a pretty clean mist cycle. Last grow I ended up averaging around 0.6to 0.7 seconds of ON time and roughly 40 to 80 seconds of OFF time. The other thing was that newly transplanted plants seemed to need direct spray until they got adapted to the new environment when switching over from mini perlite “hempy buckets” I use to start seeds.

So… Im seriously considering going with the shortest ON time I can, but have matching short OFF times. That would be 0.2 seconds ON and somewhere around 20 seconds of OFF time. I will need to test that.

Im also trying to come up with a super cheap way to cool my rez water so I can start some trial runs while its still way too hot. My grow room stays in the low 70’s to the low 80’s during the summer months. I would prefer to keep water temps down under 70, but I dont have AC in that room and no good way to add it. Im considering getting a cheap used mini-fridge or similar and see if I can rig a way to keep a smaller rez inside it while its hot.

More later…


The new root chamber is almost ready to go. I cant wait to see what happens when I turn on the sprayer…


Oh boy, stand back when you do turn on the sprayer! Looked like it could get explosive. :scream_cat: