Yeah, that is exactly what the DWC guys claim while the Aero/NFT and Membrane guy all claim just the opposite.
I vaguely remember reading about Heath Robinson or maybe I watched some videos - cant remember. I will look him up later and check it out - thanks!
In any case, I don think anyone has actually done a side by side test like Im trying to do - where (almost) the only variable is the type of hydro. In every case I have read about, someone tries various techniques and when they get a big yield, they stick to that technique - saying its “best”. The question is - was it the type of hydro or did they change nutes or temps or PH or lights or the phenotype, or, or, or?
Ive been offered some S1 fem seeds to try in this experiment by a very generous OG member!!. That will simplify what Im doing a bunch and hopefully make the results a little more trust worthy.
Its been 3 hours, so here is a progress report on the “drying” speed of the perlite and lava rocks.
Lave rocks = 19.6 grams dry and 20.9 g wet = roughly 7% water by weight
Perlite = 6.2 grams dry.and 17,7 g wet = roughly 185% water by weight.
After 3 hrs:
Lava = 20.5 g (lost ,4 g)
Perlite = 17.4 g (lost .5 g)
I cant get any decent pics of the perlite - its too white to show any contrast with my cam. Here are some dry and wet pics of the lava rock so far. After 3 hours it still looks very wet at the small scale.
Dry at 7:43 AM
Wet at 7:47 AM
Still wet at 11:25 AM
It occurs to me I should have done this comparison by volume instead of by weight, but Im not going to start over
Not sure about your experiment but it looks like your having fun dude. My take is that a medium like rock wool or perlite left to even partially dry out will remain too soggy to allow much oxygen exchange meanwhile oxygen levels in the water still in contact with roots is running low. A constant flow avoids this loss of oxygen around the roots and keeps them at a more consistent temperature. A
A very generous offer. Fem seeds will definitely help your logistics when it comes to dealing with males in the totes.
I do want to say a true S1 is where the plant pollinated itself. If this is indeed what you have, you will see lots of variation. In fact making an S1 is a good way to see what recessive traits are hidden in a genetic pool.
The term is often misused, heck it isn’t even really used outside of stoner science. A cross of two different cultivars, regardless of if they are feminized or not, is a F1 not an S1.
Good points and that lines up (sort of) with the Membrane Meniscus theory - except for the hi flow rates. He is of the opinion that you dont need hi flow rates if the roots get enough oxygen. The other thing about the Membrane theory is he also says you dont need hi PPMs - much like Heath Robinson - as long as the O2 levels are good and the water is kept to a minimum thickness (thats the meniscus part) on the roots.
I think its interesting that they both came to the same conclusion but with very different approaches and flow rates.
I forgot about the drying experiment for most of the day - got sidetracked by my 7 yr old granddaughter. She is very very good at that!
Anyway, here are the results as of 8:20 PM - roughly 11 hours since they were dunked in water.
The lava rocks have lost most of their water, but not all. Weight is down to 19.8 gm, so they have lost 1.1 gm of the 1.3 they started out with or roughly 85% of the water is gone and 15% is still there.
The Perlite is still holding a ton of water. It still weighs 16.6 gms, Interestingly they both have lost the same amount of water = 1.1 gm, but the perlite held so much more at the start that it is still very wet in comparison to the lava.
Even though the lava rock has lost the bulk of its water, it still looks wet under the scope.
Bottom line here is that I dont think there is nearly as much drying between floods as most folks think.
I got another detail done on my rez - I added a heat sink on the side for future addition of some peltier coolers if the rez temps get too hi.
I think peltier coolers are very ‘cool’ gizmos and Im actually half way hoping I need to buy some to keep the rez temps down. They are cheap and easy to work with. The cheap ones dont have perfect reviews, but it will still be interesting to try them out to see how effective they can be at cooling. One of the best features is that by simply reversing the current flow you can heat the rez. I have an STC1000 temp switch that can do that already. I wil be using it to monitor rez temps and - if needed - control the peltier coolers.
This heat sink has room for 4 of them if needed. This is just some scrap aluminum channel left over from other projects - including my Solstrip light fixture. I will attach the cooler modules to the heat sink on the outside of the tote, then attach another piece of the channel to them and add a computer fan for cooling. I have several power supplies from my RC hobby that can run them, so it wont cost much to do this. These can be had for even less on ebay.
All I did was cut out a strip 1.75" wide by 7" tall, then glued the heat sink in with 3M 5200 marine sealant. That stuff will last forever and not leak.
Im going to have to quit answering posts when Im half stoned. I keep forgetting to get to my main point. Maybe I should wait till Im all the way stoned…
Anyway, what I wanted to say was back to your comments about O2 at the roots and how it can get stale. I think you are absolutely correct on that. The Membrane guy also goes into that a lot. One of the key points he pushes is to be sure there is a fresh air supply to the root zone.
I have read in several places where people say they like E/F because it sucks fresh air into the root zone on every ebb cycle. However, if the cycles are far apart and/or dont happen over night, the O2 levels in the root zone will drop - just as you said, potentially starving the roots of O2
I was wondering if thats one of the reasons people sometimes have more success with DWC? I think its possible that waiting a long time between floods in an E/F setup could be starving the roots of O2.
In DWC on the other hand, the root zone is constantly refreshed with fresh air from the airstones.
Thats one of the things I want to pay special attention to in this design.
In the E/F tote, the way the airlift pump works will end up constantly pumping fresh air into the root zone. In addition, I plan to add vents so that any air sucked in by the ebb cycle will come from under the work bench. As I said above, I dont want warm air from the grow tent getting into the root zone.
On the other two totes, I also plan to add vents to the under side. On top of that, I am going to run a hose from the intake side of the airpump to both totes. That way, the air pump will constantly draw fresh air into the root zones in both totes.
Seems like you got the idea, it’s the usual case of find the weakest link in the chain and it often seems to be oxygen, that’s why folk like me started using hydrogen peroxide and large capacity air pumps. I found it all a real pain in the butt to be honest. The nutrient heater was always fighting the cold being introduced by the air pump and in winter the heater would sometimes lose the fight. Blockages almost daily when the roots went mad became my biggest problem, especially in loft grows which could flood the house below if things went badly wrong. Also noise from all the pumps running became a problem so in the end i went back to compost grows. If i had a garage available I would run a DWC setup but that’s just not an option. A
Yeh compost is just too easy, not enough of a challenge there lol. Check out these guys, they must deal with the boredom by making videos https://www.youtube.com/watch?v=lkgmrQicXKw
Interested in these TEC controllers. I am under the impression they are terribly inefficient, so I stayed away from them. Would like to see how they work for your application.
The ones I Linked to and the similar ones on ebay are cheap clones or knock offs Im sure. The reviews are pretty consistently at least ok, but lots of reports of units not working or not working very well.
There are much more $$$ versions available from Mouser, Digikey, etc that Im sure work mush better.
If I get some extra bucks after I get this project going I may order a set of 5 just for the heck of it
For me it was the power supplies and heat sinks that make them so expensive. I ended up spending the money on power supplies, heat sinks, and COBs instead.
Yeah, if you dont have those things on hand it can get $. I happen to have several 12-24 volt, adjustable, regulated power supplies. Enough for me to run a dozen or more of these I think, plus plenty of scrap alum channel I will use as the sinks. I cant find my computer fans at the moment, so that may be an issue.
This would still be cheaper than going with an aquarium chiller (same tech) or some other finished/pre-built chiller I think.
I am having doubts and reservations about the Membrane Meniscus technique.
I decided to run some more tests based on how I plan to setup the Membrane tote. I have been planning to follow the original patent drawings and details pretty closely.
That would be a layer of perlite in the bottom of the tote, with a water inlet on one end and a drain on the other end. The nute solution is supposed to flow slooooly through the perlite. The water level needs to be just at or barely below the top of the perlite. The, the “membrane” sits on top of the perlite. Its purpose is to allow water to wick up to the root zone but prevent the roots from getting into the perlite. The roots are NOT supposed to be sitting in water. Only a thin film of water - the meniscus - is supposed to be touching the roots.
That all sounded good to me, and when I ran my first test of the rip-stop nylon I have using just water, it seemed to work fine. That test was just filling a jar to the top with water and setting the nylon on the top and then placing a cardboard tube on the nylon and seeing the water wick up the tube. That worked ok, but the water was actually touching the nylon in that test.
I put some perlite in a jar and added water almost to the very top of the perlite. Then placed the nylon on that and stick another cardboard tube in there with a small weight to hold it against the nylon and perlite. Wicking does occur, but it is really sloooooooooooooow. Im having a hard time imagining this will be enough water to let a plant grow properly.
So I ran a second test using the silk screen. It lets water flow through it very freely where the nylon does not. The wicking action is much better, but its still pretty darn slow.
It looks like my nylon just doesnt wick fast enough to work, so maybe I have the wrong kind of rip-stop or its too dense or something. The silk screen however, is a lot more porous than what he describes as the perfect material - I think.
Im going to have to go re-read his notes and details to see if I missed something. If it wasnt for the rave reviews I read and pics from several different growers, I would doubt this could possibly work. Actually, Im doubting anyway…
Left is the rip-stop and right is the silk screen after about 15 minutes.
Good points both of you. I havent had time to go back through his details. Im pretty sure he had a test in there somewhere to show if things were wicking fast enough. Need to go back and find that.
Also, I am pretty sure he revised the technique in later years to use marine carpet for the nutes to flow through instead of perlite. That creates a smoother surface with more contact area which would make for better wicking. I think he also recommended raising the water level so it just touches the membrane.
Need to go do more reading before I build this tote…
