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Old 09-26-2018, 02:38 AM #1
Douglas.Curtis
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Tending Your Reservoir for a Full pH Swing and Cleaner Cannabis

This is how I understand using a full pH swing to grow clean hydroponic cannabis. Full pH swing cannabis is grown by providing a 'swing' in root-zone pH, from the lowest healthy pH range for cannabis to the highest.

** Notice: I only recommend using water as clean as reverse osmosis filtered water. A pH of 7 and a ppm up to 14. This information regarding res management is specific to r/o quality water being used. Any other type of water has a large potential to cause reactions which are different than what I've posted here. **

I'm a Full pH Swing Cannabis Kind of Guy
I am of the studied opinion, full pH swing grown cannabis is vastly superior in quality to steady pH (buffered) grown cannabis. In my experience the last decade, high transpiration, a full and healthy pH swing in the root zone and a balanced nutrient profile are integrated keys to growing low nutrient strength, superior quality cannabis. My goal is to share the insights I've gained, so your hydro experience is both simplified and extraordinary. I urge anyone interested in growing a higher quality of cannabis to read it completely.

Cannabis the Cleaning Plant
I find myself unable to discuss cannabis and hydroponics, without also addressing how cannabis is useful for "Phytoremediation." Phytoremediation is a big word for the process of using plants to remove unwanted elements/toxins from soil. We're all aware cannabis has unique properties in chemical makeup, but most are not aware it also has additional methods of nutrient absorption than your average garden fruit/veggie. While cucumbers, strawberries and potatoes enjoy only the 'passive ionic uptake' pathway of gathering NPK and micros, cannabis enjoys additional pathways of uptake. These additional pathways are capable of absorbing additional things from the root zone, including elements in excess, heavy metals, and toxins the plant does not need for growth. These excess elements must be converted or cannabis can, and will, affix them to new tissue growth unconverted. Should you have toxins or heavy metals in your root zone, there's a good chance cannabis will absorb and preserve it for you till long after harvest.

So the way I look at it is this. When the root zone of the cannabis plant has excess elements available, it is capable of absorbing some or all of them. When these elements are absorbed and un-needed, they are bound to new tissue without being converted. (Like a painting crew being told to paint the leftover 15 gallons on walls to get rid of it.) When bound in this way, these elements will never be released by the plant during any length of 'fade' or 'flush.' (Paint still in cans would be cleaned out in a fade or flush.) The only way I know to avoid this, is to supply only the bare minimum NPK/micros the cannabis plant needs, as it needs them, at a level which barely sustains full and vigorous growth. The best way I know how to accomplish this, is by providing very low nutrient strength solution (balanced for cannabis), with a full and healthy pH swing in the root zone. The way I have learned to control this pH swing easily and consistently, is through specific reservoir management practices. When you know how to tend a reservoir for a full and natural pH swing, you will know an easier way to approach hydroponics and cannabis. As an added bonus, the quality increase is truly amazing.

The Confusion Surrounding "pH for Hydroponic Cannabis"
So to begin we need to clear a bit of confusion around the whole subject of "the perfect pH for cannabis." I have personally watched a lot of confusion regarding cannabis and hydroponics for almost 2 decades, and pH has been at the center of most of it. There are two main points which drive this mass of confusion regarding pH.

The first point is the idea one can pinpoint the perfect pH for a hydroponic nutrient solution without regard for environmental conditions, the type of hydro setup being used and so on. Granted, cannabis does have a closely defined 'healthy' pH range in the root zone between 5.3ish and 5.9ish, so these are the targets we need to shoot for. What's needed is to change the discussion from "What's the Ideal pH for hydroponic cannabis," to "What nutrient solution pH for 'this system,media,environment' will result in our desired root zone pH?"

The second point of confusion is including all hydro systems in the phrase "hydroponics", when in reality there are at least 2 major types of hydroponic systems, each which has pH addressed differently. I've taken to calling these two systems "Roots-In," where plant roots are constantly exposed to nutrient solution, and "Roots-Out," where the roots are exposed to air between waterings, typically growing within some type of media. Roots-in systems require the nutrient solution itself to drift the entire healthy range of pH. Roots-out systems require a more narrow nutrient solution pH window, with the lower healthy root zone pH being reached through evaporation. A subtle yet very important difference. One pH range does not 'fit all hydro.'

Transpiration: Keeping Things Moving
With a further understanding of pH behind us, we also have to include transpiration. Transpiration in cannabis is controlled mainly through the action of the plant attempting to cool or hydrate itself. It is important to have a high rate of transpiration, while also making sure the rate is acceptable for the plant. When a plant experiences temperatures above 70F'ish (I don't know the exact temp), it begins transpiring water to cool itself through evaporation. When a plant is exposed to conditions it considers too dry, it uses transpiration to keep it's tissue hydrated. What we want to avoid is having the plant use maximum transpiration for both cooling and hydration due to stress. When temps and humidity are both low, cannabis uses high transpiration rates to stay hydrated. When temps and humidity are high, cannabis uses high transpiration to stay cool. The standard advice of 75F and 55% RH is a happy medium which can be reached by most growers, providing high transpiration through moderate levels of both cooling and hydration.

What's Changing the pH?
The pH in a nutrient solution is affected by several things, the amount of nutrients, evaporation, biological activity, root rot, and other environmental inputs. The main pH changers are the amount of nutrients in solution which is affected by adding nutrients and plants removing nutrients. The addition of nutrients drops the pH, while the action of plants using the nutrients causes this pH drop to reverse. When the ppm/ec goes up, the pH drops, and as the ppm/ec goes down, the pH rises. Evaporation of water from the nutrient solution also causes ppm/ec to go up, dropping pH. Adding water to a reservoir (topping off) will also lower ppm/ec and slightly raise pH. The growth of algae/bacteria/fungi can quickly drop pH. Root rot, depending on how severe, can cause a slow drop to a fast crash in pH. Last, but not least, environmental factors such as too much aeration of the solution can also raise the pH.

How fast the pH swings is controlled by reservoir size. For any given combination of light and plants, decreasing your solution volume will speed up the pH change. Increasing the volume will slow down the pH change. The more solution you have, the longer it will take the plants to use nutrients from it and the slower the drop in pH will be.

Roots-In Hydro Systems

Let's jump right in and go over management of a roots-in reservoir, then we'll cover roots-out reservoirs. Roots-in hydro has the least number of variables where pH is concerned, and is my personal favorite.

Mixing the Reservoir for Roots-In Hydro
Since pH drifts up as plants use the nutrients in solution, we want to start our pH at the low end of the healthy root zone pH. I advise topping off reservoirs daily, since this helps keep track of transpiration rates. Allowing the nutrient solution level to drop also causes a slight pH drop, along with exposing the roots to a bit more air for a little while.

  • Fill with r/o water to desired nutrient solution level (Mark this level, so you know where it is)
  • Add your base nutrients to within 50ppm of your target
  • Add pH up to reach 5.4 (float valve top-off, roots-in systems would start at 5.3)

Daily Reservoir Tending for Roots-In Hydro

  • Re-fill your reservoir back to the mark with r/o quality water
  • Record transpiration rate
  • Check and record pH and ppm/ec
  • Check and record solution temp
You're checking the solution temp to be sure it stays within 65F-69F. I've used these temp ranges for 15+ years and strongly recommend them to significantly reduce headaches and the use of additional resources. Anyone not able to tightly control solution temperatures should be using a roots-out hydro system. Roots-out systems can handle much higher nutrient solution temperatures, up to the low 80's depending on the setup.

Over time you will notice the pH go up and the ppm/ec go down. It should take about 7-10 days for the pH to swing from 5.4 to 5.9-6.0. When your pH hits the top healthy range for your specific plants/setup, add your nutrients back until you reach your starting target ppm/ec. You'll find your pH is back at the starting point when you mixed your reservoir. You have reset the pH and started the upward swing again. Bam! That's 90% of it right there. Lather, rinse, repeat until major flower bulking stops and transpiration suddenly slows. What to do at this point? Skip to the 'Fade' section after the roots-out section. It's the same for all hydro systems, so I put it at the end.

Roots-Out Hydro Systems

Roots-out hydro systems provide a larger pH swing between waterings, which brings a slightly larger change in ppm/ec as well. The pH starting point will be higher, according to how much of a pH drop there is in the root zone. Each system/environment/genetics choice will cause this pH drop to be higher or lower, making roots-out systems a bit more complex to dial in perfectly.

Mixing the Reservoir for Roots-Out Hydro
  • Fill with r/o water to desired nutrient solution level (Mark this level, so you know where it is)
  • Add your base nutrients to within 100ppm of your target
  • Add pH up to reach 5.5-5.6
Daily Reservoir Tending for Roots-Out Hydro
  • Re-fill your reservoir back to the mark with r/o quality water
  • Record transpiration rate
  • Check and record pH and ppm/ec
Over time you will notice the pH go up and the ppm/ec go down. It should take about 7-10 days for the pH to swing from where you started to reach 6.0-6.1. The top healthy solution pH will depend on your system and genetics. When your pH hits the top healthy range for your specific plants, add your nutrients back until you reach your starting target ppm/ec. You'll find your pH is back at the starting point when you first mixed your reservoir. You have reset the pH and started the upward swing again. Bam! That's 90% of it right there. Lather, rinse, repeat until major flower bulking stops and transpiration suddenly slows.

The Fade (All Hydro Systems)
When your plants switch to oil production you'll notice a drop in the transpiration rate. Where you were adding back 3-4 gallons of r/o water a day, you're now only putting in 2. This is the point you need to lower the nutrient solution strength, so the transpiration rate is kept near what it was previously. A system using 5 gallons of water a day at peak flower production, should still be using 3-4 gallons of water during oil production.

  • Note your current pH
  • Remove nutrient solution from the reservoir and replace with pure r/o
  • Re-pH the solution back to the note you made
  • Check transpiration daily

Your goal is to keep the pH swing from being interrupted, while you keep transpiration at a moderate to high rate. This is kept up until 5-7 days before harvest and then we start the flush.

The Flush
So you've been fading the plants as you've kept transpiration rates up, and you're now 7 days from harvest. This is the only time you will dump your reservoir during a flowering run. The solution strength should be rather low and is awesome for gardens and lawns. Pump it out and use it well, then re-fill the reservoir with pure r/o. Over the next 7 days you'll notice the ppm/ec rise a little as osmosis pulls nutrients back out of the plants. Continue topping off daily with r/o until harvest.

A Note on Additives
You may have noticed I did not list any additives, nor do I mention when/how to use them. I personally only use NPK/Micros and a tiny bit of a fulvic acid product. Additives can cause pH changes to happen differently than described here. Some additives increase pH quite a bit, setting up a pH drop as they're used up, while others do the same in reverse. I strongly recommend running your reservoir without additives a few times. Once you're familiar with keeping the swing going, you can experiment with your own personal additive choices and adapt your management techniques to fit. What's important is a full and complete pH swing, within a 7-10 day period. If you can do this with your favorite additive, more power to you.

I challenge anyone who's never grown with 'just' NPK/micros to do so at least once or twice. You'll most likely be extremely surprised with the quality cannabis produces with the bare minimum.

Any questions?
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Old 09-26-2018, 12:36 PM #2
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Very interesting! Thanks for sharing!
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Old 09-26-2018, 02:36 PM #3
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My pleasure.
Wish I could have 'just' posted res tending info, but everything here is necessary info. lol Everything is so tightly integrated there's no separating them.

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Old 09-26-2018, 04:18 PM #4
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Nice post Douglas.Curtis I like the way you describe the plants taking the extra nutes and storing them "(Like a painting crew being told to paint the leftover 15 gallons on walls to get rid of it.)"

Make me think of all these dispensary growers who max out the nutes at flower, then have horrible tasting weed with no nose.
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Old 09-26-2018, 04:25 PM #5
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Allowing your pH to swing from ~5.6 up to ~6.3 and then readjusting to repeat is one of the secrets of growing that many people don't know about. It makes all the difference in the world. It's not a folk tale or anything... it's science.



In certain pH points, some nutrients are at least partially unavailable, so by letting the pH swing naturally you are making sure the plants get all the nutrient availability. I learned this early on and it makes a big difference in the quality of the plants. It's easier to do with a recirculating hydroponics reservoir, but I've done it before with a DTW setup (hempys) and it required artificially swinging the pH.

That's another reason I prefer recirculating hydroponics.
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Old 09-26-2018, 10:44 PM #6
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Quote:
Originally Posted by Hydro8 View Post
Nice post Douglas.Curtis I like the way you describe the plants taking the extra nutes and storing them "(Like a painting crew being told to paint the leftover 15 gallons on walls to get rid of it.)"
Thank you. I've been thinking about this subject for nearly a decade now. I'm glad the analogy I finally came up with works for you.

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Originally Posted by Hydro8 View Post
Make me think of all these dispensary growers who max out the nutes at flower, then have horrible tasting weed with no nose.
Exactly! I cringe when I see the typical feeding chart for cannabis. I've come across very few dispensaries selling cannabis without the overfed experience.

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Originally Posted by hush View Post
Allowing your pH to swing from ~5.6 up to ~6.2 and then readjusting to repeat is one of the secrets of growing that many people don't know about. It makes all the difference in the world. It's not a folk tale or anything... it's science.
Right on the money.
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Old 09-27-2018, 07:11 AM #7
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Great info, guys
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Old 09-29-2018, 12:17 AM #8
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Thanks Robbie.



I wanted to add:

Though I have not personally explored the option, I am aware the possibility looks promising. I have run across a few growers who use the opposite pH swing method, through not topping off the reservoir regularly.

This method employs a pH drop, vs. the normal pH rise. The reservoir strength starts out low, with the pH high. Exactly the opposite of the strength high, pH low method I outlined. As transpiration and evaporation happen, the ppm/ec increases and drops the pH. When the pH hits 4.3'ish, you would refill the reservoir with the same strength nutes/pH you started with.


Since I have not personally used this method, I urge anyone who has to post their personal experience.
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Old 09-29-2018, 12:33 AM #9
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Originally Posted by Douglas.Curtis View Post
This method employs a pH drop, vs. the normal pH rise. The reservoir strength starts out low, with the pH high. Exactly the opposite of the strength high, pH low method I outlined. As transpiration and evaporation happen, the ppm/ec increases and drops the pH. When the pH hits 4.3'ish, you would refill the reservoir with the same strength nutes/pH you started with.
I have always been uncomfortable when my ph gets below 5.5. I read somewhere that pythium like lower ph.

Not sure on this just something I have read and has stuck in my head. Do you have any insight on low ph and pythium ?
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Old 09-29-2018, 03:52 PM #10
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Quote:
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I have always been uncomfortable when my ph gets below 5.5. I read somewhere that pythium like lower ph.

Not sure on this just something I have read and has stuck in my head. Do you have any insight on low ph and pythium ?
In 15+ years, I have not seen any pythium on my vegging or flowering plants. I have had clones/seedlings damp off, due to poor conditions, but no vegging plants in hydro. I've witnessed PM on my plants once, when my veg area was too humid and had slow moving air.


So personally I haven't seen a connection.
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