Pathogen Control

Edit: I had to edit this entire post, because I realized that I was regurgitating some of what I've read, and after posting I realized there were basic chemistry mistakes I repeated from even reputable sources about the precipitation of nutrients. I will also continue to edit this as I find other misinformation or more useful information

Sterilization methods

UV light

UV is probably one of the best sterilizers there is in terms of water in the nutrient tank. As water is circulated through it is exposed to UV radiation which alters the DNA of any pathogens and kills them. This will not kill any bacteria that have colonized the roots or the surfaces of your system.

It is necessary to maintain a clear reservoir free of floating debris through mechanical filtration otherwise the pathogens may hide behind the debris and manage to live.

I previously stated that UV light causes precipitation of minerals, this is simply not true unless you are generating ozone with UV light.

Before I go into the other methods of sterilization, I would first like to explain the chemistry behind them. Basically, any chemical sterilizer is oxidizing pathogens. The concentration/ability of the particular chemical to do this is measured by Oxidation Reduction Potential (ORP).

Oxidation Reduction Potential(ORP)

First, it doesn't measure the amount of oxygen in your water.

As a quick chemistry lesson, with very unfortunate semantics, I will explain what is pertinent.

To help you remember we will use the acronym OILRIG

Oxidation Is Losing (electrons), Reduction Is Gaining (electrons)

The ORP is the ability of the nutrient solution to "oxidize" pathogens present in the water. This means they steal an electron from the pathogen.

[Oxidizer + pathogen(electron) -------> no_longer_oxidizer(electron) + dead_pathogen] The oxidizer is reduced, it gained an electron. The pathogen is oxidized, it lost an electron. End result, pathogen dies.

Before anyone running aquaponics smacks me with their dead fish, they need to stay at less than or equal to 300mV ORP.

For everyone else, ORP levels of 700mV are recommended for horticultural irrigation water.

Source: Greenhouse and Nursery Management Practices to Protect Water Quality
By Julie Newman (page 108

Albeit I believe they can run higher, up to 825mV.
Source: http://ghex.colostate.edu/pdf_files/DisinfectingWater.pdf

Also, don't exceed these guidelines. Oxidizers are not discriminatory, they will oxidize anything, including your plant and that can hurt it.

Furthermore, in the instance of iron in your nutrient solution, any oxidizer to will some extent oxidize the iron into "rust" which will precipitate out of the solution. After all, rust is just a positively charged iron ion and if you take electrons from it then it will become rust. Some other elements, I believe one is Manganese, will also be precipitated by oxidation.

It is necessary to add these elements back into the nutrient solution or to change the solution regularly or to start out with a higher initial concentration - it all depends and I don't have a "rule of thumb" on this one.

There are ORP controllers which can be used with injection of any of these chemicals. Alternatively, one can buy an ORP "pen" a bit cheaper and dose yourself - but you never know what happens when you're gone.

Hydrogen Peroxide

Hydrogen Peroxide doesn't last very long in the reservoir so it needs to be added frequently to be effective. This can be accomplished with a peristaltic pump and ORP controller. It breaks down into water and oxygen fairly quickly.

Chlorine

Chlorine will form Cl2 poisonous gas at a pH below 6. You're probably using such low amounts this wont cause any issues, except for that it will no longer be in the reservoir cleaning. Nonetheless, it is recommended then for hydro to stay between 6.0 and 6.2 pH

Most growers I see just say "add x amount per every couple of days"

This is very poor advice, and I will explain why

1. pH may cause the chlorine to leave quickly
2. Free chlorine vs total chlorine

a. Free chlorine is chlorine that is available to react. It is chlorine that is in the reservoir and ready to oxidize any pathogens it comes across.

b. Total chlorine is the total amount of chlorine, in various forms, in the reservoir. What happens is that when the free chlorine attacks a pathogen or other organic material it loses its ability to oxidize further pathogens. So total chlorine is free chlorine , "used up" chlorine, and other forms not useful to us.

So at minimum you need to check both free and total chlorine. There are test strips available but their accuracy varies. The general consensus is that 0.5ppm of FREE chlorine is necessary to maintain an uninfected reservoir.

However, you can't just keep adding chlorine as once you get to 20ppm of total chlorine cannabis will begin to show signs of chlorine toxicity.

So you see, the amount of chlorine depends not only on volume but also on biological load.

An even better way, albeit more expensive, is to monitor the ORP with chlorine as well.

Peroxyacetic Acid or Peracetic Acid

This is a combination of chlorine and hydrogen peroxide. When you combine the two in a one to one ratio you ended up with peracetic acid and water. The one to one ratio is not volume, it is molar.

If you were to use the safe to ship hydrogen peroxide which is 17.5% one mole would be

1 mole = (34.0147 grams/mol)/(0.175 which is the concentration)/(1.06g/mL (specific density of 17.5% hydrogen peroxide)) =~ 183mL per mol

If you use glacial acetic acid then

1 mole = (60.05 grams/mol)/(.9985 which is a concentration of one brand I saw on ebay)/(1.05 which is the specific density for that particular brand) =~ 57mL per mol

You can use different concentrations, just change the percent with 1 is 100% and .95 is 95% and .5 is 50% etc.
Peracetic acid is a stronger oxidiser than hydrogen peroxide and a weaker acid than acetic acid plus it's more stable than hydrogen peroxide. End result is that it will perform well at the pH that you run for this plant and have a wider reaching effect on components of the hydroponic system and last a bit longer..so it saves you money.

Ozone

Ozone is one of the strongest oxidizers. Monitoring the levels require an ORP controller to ensure correct levels. Good info: http://www.hydroponics.com.au/issue-36-introduction-to-ozone-generation/

The Slime

I lost two batches of clones to this stuff, despite using EWC tea. In order to help those who may be having some issues, I would like to help you identify if you have an issue.

Note: I may have added too much molasses to the tea, and I didn't clean anything prior to introducing the tea so the pathogen may have overwhelmed the beneficial microbes.

Here it is on one of my cloner nozzles:

Here it is on a clipping:


Now while I didn't take a culture off of the clipping, I did take one off of the mister, here it is (dyed blue since it was white) under a microscope at 600 times magnification:


Here another, slightly more focused:


Now, I also previously had a slimy feeling brownish growth in my reservoir (no nutrients or anything and filtered through RO). Now I have it above the water line again despite 1mL of bleach per 15 gallons every three days. Why? Because as I explained in my last post, you can't just dose an oxidizing chemical by volume.


Here it is under the microscope:




Both Heisenberg and Richyrich attribute this "slime" to brown slime algae also known as Dinoflagellates. I'm not sure if this is the case, as it resembles more iron bacteria.

How does it turn it turn white?

Well, iron bacteria is only orange/red when it has iron to eat. It can not move on its own, so it relies on your water circulation to carry it somewhere. It forms a "biofilm" or sticky surface and will stick to whatever it can "including your plants" but it is unable to take iron from your cuttings or your misters.

It is also capable of oxidizing maganese. Boy, this iron bacteria can be more troublesome than oxidizing chemicals.

I thought only wells could get this?

It's a bacteria, it's outside, somehow you introduced it into your room. Congratulations, you may be able to control it with beneficial bacteria. If you keep your "grow zone" immaculate you can kill off any of the bacteria with a UV light recirculating in your reservoir. Otherwise, dose with oxidizing chemicals. Or, you might even have a well.

Are you really sure it's iron bacteria?

Have a looksie yourself: http://www.wellrehabilitationsolutions.com/about-boresaver/what-is-iron-biofouling/

I put a glass and caught some of the return water from the cloner. This is what I found, here are two groups of iron bacteria at 60, 150, and 600 times magnification respectively.

Numero uno




Numero dos

Wow... a post with substance on RUI from a newer member...


Unheard of!


Welcome to the forum bruh

I'm all for short wave ultraviolet lamps for germicidal control, seen how useful they are in labs which deal with bac samples~

wiki:
Ultraviolet CUVC280 – 100 nm4.43 – 12.4 eV

**nice pics of the bacteria

Thanks hydro!

Thanks canna!

I was starting to think no one gave a crap about this information and I was frustrated I spent the time to type it up/took the bacteria photos and posted them instead of just viewing it myself.

Although I wish I had better pics of the bacteria, but I can only go up to 600x magnification. I'm using a kids microscope LOL and then just a generic microscope camera at 3 megapixels.

Vostok, I have edited the material to try and fix some of the misinformation, including that UV light will oxidize minerals and cause them to precipitate out of solution. I'm not posting groundbreaking new material I'm just providing information in a more digestible form that others in this forum may find useful condensed at on location.

I see the pictures of iron bacteria. How does it get into the water? With wells, it usually happens during drilling or could happen during servicing. This is how it can also get into your grow - you could track it in, put it in with some compost tea, etc. With wells, why doesn't it clog up your well then, I mean, look at all that sludge in the pipes you posted? Well first, to be orange/red it needs enough iron and secondly it needs oxygen. This would explain why it is so easily able to colonize the aero systems, they're very oxygenated. I don't have any issues in my DTW with it which was right next to my aero cloner and I spilled some of the contaminated water in. The red can only happen if there's enough iron "Iron bacteria produce a sticky slime which is typically rusty in color, but may be yellow, brown, or grey." - wikipedia It can also eat manganese and will present in black color.

Perhaps the RO doesn't filter it out, perhaps you have some metal components in your system that they're feeding off, perhaps you spilled some nutes..it doesn't take much to somehow get in there.

There are two types of brown slime algae - one is diatoms..they look like big pills under a microscope at the magnification I used. The other does look similar to the iron bacteria, but it can move on its own I believe, and I didn't see any self propulsion under my scope even with the live cultures in the reservoir. This is why I don't think it's brown slime algae like richyrich and heisenberg say.

Some more thoughts:

Hydrogen peroxide

In concentrations high enough to kill viruses it will also kill your plants for sure. UV light will kill bacteria but it will also turn hydrogen peroxide into OH- ions which will raise your pH and if you use pH down then you just turned it back into water.

Peroxyacetic acid

If you have a concentrate solution, which will be an equilibrium reaction between hydrogen peroxide, acetic acid, and peroxyacetic acid..and then you heat it or otherwise remove the acetic acid so that the concetration of peroxyacetic acid is 50% or greater it will go boom..so be careful.

Secondly, aside from just adding them together, you need a certain amount of sulfuric acid to catalyze the reaction.

Third, it isn't stable, the peracetic acid will break down back into hydrogen peroxide and acetic acid in just a few hours. I know there are commercial versions which have stabilized it but the only two ways I know involve picoclinic acid or dipicoclinic acid and I think it depends on how you make the peracetic acid (it can be made a few ways) as to which one you should use. Even then, it will all break down after about a week if you have a ~12% solution. Except at room temperature if you just mix it all together even with the sulfuric acid I believe it takes a week to reach equilibrium to begin with. So without a way to stabilize it better (there may be) I don't think this is viable at the time.

Ozone

If you inject ozone into your reservoir in order to not gas out into the atmosphere you need a reservoir about 7 foot deep. You can also inject it with a venturi but I'd be nervous about its compatibility with pumps, pipes/tubing, etc. even at lower levels.

ORP Controlling

I previously recommended ~700mV. Well that is for a chlorine based oxidizer. The nernst equation shows that different chemicals oxidation potentials affect the reading on the ORP meter, i.e., a stronger oxidizer will be equally effective at a lower mV and may or may not be too strong at 700mV.

So, at this time, chlorine is the solution that I believe makes the most sense provided you keep pH at 6-6.2 and no lower to prevent chlorine gassing off and further monitor to prevent it from accumulating in excess of 20ppm total to where it will be bad for this particular plant.

Peroxyacetic acid is really superior, provided you find the right mV necessary, you could run a reservoir indefinitely - it's even more effective with UV (it's more UV stable than hydrogen peroxide)- provided you added back the missing nutrients with the utilization of a photometer to tell you what is missing. To do this, the acid must somehow be stabilized.

Note: whatever chemical you use, if you are using an injector - check all of the materials for tolerance with that chemical or you could end up with a mess on your floor.

Further research has shown that UV and ozone will both cause precipitation of iron and manganese. I have been running some experiments with ORP and calcium hypochlorite. I have included the data below. While I did not try to confirm the previous experiments by USDA it should be noted that utilizing citric acid has been shown to interfere with hypochlorous acid and result in a low ORP at normal chlorine concentrations which will either result in high chlorine concentrations or long kill times. Other studies say the same about using stabilized chlorine, as it contains cyanuric acid (trichlor or dichlor), however to my knowledge this has not been used for irrigation purposes but just for pools.


Calibration: pH meter was calibrated to 6.9 and then to 4.00 prior to use. ORP handheld meter had just come from the factory and was already calibrated to ~100 mV. ORP doser meter was calibrated to 400mV prior to use. EC meter was also new from factory and had been calibrated prior to use. Test strips were used to check ppm free and total, their accuracy was sometimes checked against OTO titration which yielded similar results and therefore the data is omitted.

Chlorine: 1.000g of calcium hypochlorite with minimum 54% available chlorine was weighed and diluted into a 500 mL beaker. This was periodically mixed to ensure a homogenous mixture.

Water source: Water was filtered through a RO system and received recirculating UV sterilization. It should be noted that this water is stored in the grow operation and so is exposed to CO2 concentrations of 1500 ppm which resulted in a pH of ~6 due to the carbonic acid present in the water.

Vessel: 500mL of the water source was placed into a glass container containing pH meter, a handheld ORP meter, and a meter from dosing equipment. EC was checked by hand after each addition of nutrient solution with a handheld EC meter.

Count 1: Chlorine was added and some buffering was done with GH powder up and concentrated sulfuric acid. Exact amounts are unknown because I did not record them and the concentrated nature in such a small container caused me to overshoot my target several times. Neither the powdered base nor the sulfuric acid had any unexpected affects on the ORP. When the pH was raised the ORP went down as less HOCl became available and vice versa.

Counts 2-5: 100 times concentrated two part nutrient solution was added dropwise to obtain the desired EC. This occasionally caused a total loss of free and total chlorine as measured by the test strips and a corresponding drop in ORP. It is unclear if the aqueous nutrient salts caused an evaporation of chlorine or if they combined to form new compounds that weren't recognizeable as total chlorine by the test strips and OTO titration. Occasionally after addition of chlorine 1ppm of total chlorine residual was observed at the higher EC levels however there was always a corresponding drop in ORP and complete loss of free chlorine. It was necessary to add more stock chlorine solution to raise the ppm back to ~1 free ppm and as the EC was raised the necessary total chlorine went up as well. Adjusting of the pH was necessary as an increase in nutrient solution concentration correlated with a drop in pH. As is evident the ORP also dropped at similar free chlorine concentrations as EC went up. It is also of note that as EC went up the handheld and dosing meters values seemed to have less deviation from eachother.

Conclusion: It is my recommendation that in a concentrated nutrient solution utilized in a hydroponics system disenfested with hypochlorous acid on chlorine sensitive plants that an ORP of 600mV is desirable. This will result in quick kill times of pathogens while ensuring the free chlorine levels remain below 2.5ppm. Free chlorine levels of 2.5 ppm have been shown to be a safe concentration on small woody ornamental plants which are chlorine sensitive in another study where the irrigation water came from overhead sprinklers. I feel that the sub minute kill times of a 650mV+ solution may be excessive due to the frequent contact between root zone and nutrient solution as well as leave less wiggle room for errors in equipment and calibration which could potentially result in too high of chlorine concentrations for said plants especially at higher EC. Weekly calibration of meters is also desirable as well as secondary testing with test strips to ensure chlorine concentration remains at acceptable levels.

I wanted to see if I could confirm the data from the USDA that says citric acid will lower the ORP by interfering with the ability of hypochlorous acid to kill bacteria. As such I utilized GH pH down powder in an experiment where citric acid is listed as one of the ingredients. Here is the data that I collected. The first count utilized sulfuric acid, whereas the third count utilized GH pH down powder for lowering the pH.


Materials and Equipment: All materials and equipment were the same as in the previous experiment.

Methods: I have found through research that most ORP meters will have a very different initial read out, and if you're interested in corresponding measurements something like 20 minutes of immersal is necessary to get between 1-2mV variance between meters. Also, at low alkalinity measurements will be more accurate if the meters are continually moved back and forth or if there is a constant flow past the meters. In this experiment I moved the meters back and forth for an arbitrary 270 seconds in the container before taking my measurements at the ~6.2 pH. I did not for the higher pH, but wanted to include the data as full disclosure. It should be noted that the accuracy of the pH meter is only to within 0.05 and so I feel 6.2 and 6.25 are equivalent and within this tolerance.

Variable: In this experiment while the initial data was taken from a solution similarly buffered by concentrated sulfuric acid and gH up powder, the pH was then raised with GH pH up powder. None of this affected the chlorine levels in the solution. pH was then lowered using a solution of GH pH down powder dissolved in the same water source aforementioned. This reduced the chlorine to 1ppm total and 0 ppm free. Chlorine was added from stock solution to bring it back up to 1ppm free and a resulting 3ppm total.

Conclusion: It is observed that the ORP from solution buffered utilizing sulfuric acid averaged 718.5mV between the two meters. When the pH was again lowered utilizing citric acid containing GH pH up powder the average between the two meters was 677. This second reading is ~94% of the first or ~6% decrease in average ORP. Interestingly, it was the first time the handheld meter read higher than the dosing meter. I suspect had I given them more time readings would have converged between the two meters somewhere in the middle as they both were heading in that direction and is the reason for the averaging. It is unknown the actual concentration of citric acid in GH pH up powder but it is clear that it negatively affects ORP which confirms previous studies by the USDA. As such, I recommend if using a form of hypochlorous acid for nutrient solution disenfestation that GH pH up powder or other citric acid containing pH adjusters be avoided. I suspect the effect may be compounded at higher EC as it has previously been observed by myself that nutrients added into solution also reduce ORP. Sulfuric acid has shown no ill effects to ORP or levels of chlorine.

ShirkGoldbrick said:

I lost two batches of clones to this stuff, despite using EWC tea. In order to help those who may be having some issues, I would like to help you identify if you have an issue.

Note: I may have added too much molasses to the tea, and I didn't clean anything prior to introducing the tea so the pathogen may have overwhelmed the beneficial microbes.

Click to expand...

you did it wrong, and it didn't work. what a surprise.

test what happens if you add too much h202 or bleach.

sqlb3rn said:

you did it wrong, and it didn't work. what a surprise.

test what happens if you add too much h202 or bleach.

Click to expand...

I did try it again with the tea and didn't make the same mistakes in a bubble cloner. Still got the slime.

Did you try feeding the plants and making sure the roots have enough oxygen?

They were Cuttings so just water and tea. Water was 60-70 just room temperature. I had 5 12" airstones on a 300 gallon tank air pump in a 20 gallon 20x40" cloner.

lots of great info here, thanks.

wanted to add some info:

Ammonia reacts with hypochlorite to form chloramines that are exponentially less effective while sequestering your free chlorine concentration. not the case w/ nitrate, luckily.

GH liq pH down (surprisingly) has ammonia in it....along w/ all of my fav base nutes. I found recently that advance nutrient's pH down is phosphoric acid and doesn't react with my chlorine if I add it first, achieve pH 6.0, then add chlorine to 2 - 3 ppm free chlorine. Let this circulate while adding clones, but I also discovered that as I was adding my clones the free chlorine dissipated, probably b/c it's busy surface sterilizing the clones and is there as total chlroine, but not free. I should have added back free chlorine, but didn't.

It's important we achieve (as ShirkGB suggests) the pH 6.0 to push the hypochlorite to hypochlorous acids. Also, several publications I've read for greenhouse hydroponics suggests maintaining atleast 2 ppm free chlorine, pH 6.0 for (depending on the study) 30 seconds to several minutes.

One publication mentioned several plants tolerances of free chlorine. the lowest tolerance was 7.6 ppm.

I bought a new cloner recently and used my approx 1 year old permaclone collars. I pressure cooked my collars, and got 100% clones. This made it clear I'm battling a pathogen IN the cloner and not my water supply (or permaclone collars).

It should be noted the plants I cloned with successfully were also from canna coco plants. Canna coco has trichoderma that seems to prevent these problems...and possibly as the plants grow the trichodermia colonizes their epidermis, like yeast colonizes grapes.

Some nutes have organics in them and may help bacteria spread. I recently used an aero cloner and got "slimed" once my temps went over 73. Using pondzyme and hydroguard I was able to beat the slime and only lost a few clones. With the infection I dosed at 10mL/gallon of hydroguard.