Need help with nutrients


#1

So I’m starting to understand that the focus behind the OpenAg initiative is mainly on hardware and design rather than the actual growing process. However, I’ve spent over $1000 on my aeroponic system and have had it up and running for almost six months. During that time I’ve had insanely unstable pH, over fertilization at 100ppm nutrient concentration, nutrient deficiencies, and much more. Its a mess. The plants absolutely love the aeroponic system but I just can’t get them to grow perfectly. I’ve emailed over four different nutrient companies and none can help me due to my “unique” situation. I’m able to find any helpful information anywhere else on the web. I’m out of options and I’m really hoping someone here can work with me. I can’t imagine that I’m the only one having nutrient issues like this. I’ve tried using everything from General Hydroponics to Advanced Nutrient’s pH Perfect Technology. So I’d greatly appreciate any help at all. Any suggestions. Anything. Thanks!


#2

Glad someone else is pondering this. Controlling nutrient composition and delivery is a pretty important factor to the growing process. I’ve been reading about it and “cooking” on for designs to control/idiot-proof the nutrition aspect for those without green thumbs (which is me)

Can you tell me a little bit more about your growing setup? I have a few questions:

  • You mention aeroponics - I assume you are concocting or buying a nutrient solution and using a spray bottle to mist the solution over your plant roots - is that correct?
  • How are you diagnosing unstable pH/over fertilization and nutrient deficiencies? Are you experience leaf discoloration/wilting and stunted growth?
  • Are you independently verifying solution pH before applying them to your plants? There’s a myriad of pH meters available on the market you could try out. They run the gamut from cheap to expensive, here is a cheaper well reviewed one you could try. I wonder if this will help deduce whats going on re nutrient delivery in your growing apparatus…

#3

Alrighty, so here’s my setup:
I’m running a high pressure aeroponics system at 100psi. I’m using fine mist nozzles, on a timed interval, to spray my plant roots.

I use a lab grade, calibrated, digital pH meter to measure pH. I also have a PPM meter that measures up to 9999ppm.

Here’s my situation:
Upon starting the system, I used General Hydroponic nutrients at a concentration of ~400ppm to feed my plants. This quickly caused over fertilization. After reducing the concentration to 100ppm, the plants started to show nutrient deficiencies. Upon further inspection, I realized the GH nutrients weren’t pH stable at 100ppm. The pH would rise on its own. I took RO water, mixed my nutrients, then let it sit, untouched by anything and completely isolated from my system. I found that the pH would rise to 7.4 on its own. Even after the addition of pH down, the pH would still constantly rise. Keep in mind, this way when these nutes weren’t even in the system. They were just sitting in a tub not being touched by anything. So, I came to the conclusion that GH nutrients simply weren’t stable at such a low concentration.

I then discovered Advanced Nutrient’s pH Perfectly Technology brand of nutrients. These nutrients would only keep the pH stable at above a concentration above 100ppm. So, even nutrients formulated to maintain stable pH would not maintain it at such a low concentration. There’s nothing in my system that would cause pH to rise. I’ve run RO water through my system many times to clean it out and I still continue to have nutrient instability problems.

I’ve run hydroponic systems flawlessly using the same exact nutrients but just a higher concentration. So I’m confident in that I’ve limited the problem down to nutrient instability at low concentrations. Which seems very odd because surely I’m not the only one running an HPA system. What do other people use? What concentration are they using? There’s just a huge lack of information when it comes to HPA.

Edit: Here’s just one picture of how bad my plants are. It gets worse.

http://imgur.com/lvEXXnF


#4

Hmm…just spitballing here.

I’m gonna guess phosphates are culprit because:

  • They are used for plant nutrition so there’s a good chance it is in your solution

  • It has a few anionic forms each with their own ionization values (H3PO4, H2PO4-, HPO4 2-, PO4 3-)

  • All anions can have a predilection towards pulling hydrogens off of water and leaving hydroxides (OH-) behind, which are basic species. This will cause the pH to rise, which appears to be what you are experiencing.

It could be another species causing the pH drift, but regardless of what species is really the culprit, the underlying mechanism and tools you use to correct it are going to be the same.

I guess this is where solving the problem gets a little bit tricky as you will need to know the exact concentration of the species to determine what the pH of the resulting solution will be - I’m not sure that is something the nutrient solution will advertise. What is the species in the ppm figure you are referencing? If you know what the species is, you can:

  1. Lookup the ionization constant for that species from somewhere on the web
  2. Figure out your initial species concentration
  3. Set up an ICE table to calculate the equilibrium concentration of hydroxide or hydronium ions (and therefore the equilibrium pH)

So you could just work backwards - decide what pH and nutrient concentration you want the equilibrium solution to possess, fill those in in the equilibrium section of your ICE table and solve for the initial concentration as the unknown. Might have to add in some extra chemicals to modify the pH.

This will be impacted by the fact phosphates (or the real culprit species) will be slowly removed from the solution via the plant. Might have to account for that…

Does this help?


#5

This helps tremendously! Thank you. I will see what I can figure out and will report back with my results. Thanks again!


#6

KBrockman, could I email you?


#7

Yes of course! Sorry Dz, didn’t see this until now.

Shoot me an email at brockman.ks@gmail.com


#8

I`d recommend using a nutrient specifically formulated for run to waste and use the HPA system run to waste. If you have to recirculate the nutrient you are most likely delivering too much mist to the roots…From your description it sounds like you have the most basic form of HPA (pump, timer and nozzles) which tends to limit control. Typically the minimum misting duration will be 3 seconds for a basic pump driven HPA compared to 1 second when using HPA equipped with accumulator and solenoids.
Note that the timer setting and the actual mist duration rarely match so its a good idea to video one complete misting and use editting software to check the real mist duration from start to finish. Nozzles rarely deliver the stated flowrate, you should test this too so you know what your system flowrate (including losses) really is.