How to operate a sterile hydroponic system

Discussion in 'Hydroponics / Aeroponics' started by jijiandfarmgang, Oct 31, 2014.


    jijiandfarmgang Well-Known Member


    Whats the best sterilizing agent for a hydroponics reservoir?

    There are many ways to have a sterile reservoir, chlorine, H2O2, Ozone, etc. All have pros and cons. I'm going to focus on Chlorine because its easy to measure, cheap and effective.

    I have root rot/ pathogen problem how much extra chlorine should I add?

    Chlorine is best used to prevent pathogen outbreaks not to treat them.

    Is running a sterile res better than using beneficial bacteria?

    I'm no aficionado on bennies, so I couldn't say. However some claim that they tried running sterile and it didn't work for them; bennies being the only thing that works. I doubt they were properly using a sterile reservoir in the first place but who knows.

    If I don't have a sterile reservoir or use beneficial bacteria will I get a root rot/pathogen problem?

    Not necessarily. Many people claim to use neither and have great results. If you focus on using plenty of dissolved oxygen, keep nutrient solution at a reasonable temperature, use a relatively low EC, do solution change outs at reasonable intervals, keep organic material, nutrients and additives out of nutrient solution, and keep away light should be fine too.

    However, I do always recommend using bleach as a sterilizing agent in between grows.

    I heard chlorine is bad for plants?

    Not necessarily. Most plants can tolerate up to 5 ppm of chlorine.

    This is great, I found an old gallon of bleach underneath my kitchen sink. This should be enough to sterilize my reservoir for years right?

    If your going to use bleach, its better to use newer bleach. After a year the composition has drastically changed.

    My tap water has chloramine, its the same as chlorine except it doesn't dissipate as fast right?

    Not really. Chloramine is not as effective as oxidizing as chlorine.

    I heard all I need to do is add 1ppm chlorine per gallon every 2 days to my reservoir and I'm set.

    Not really. FYI most municipal tap water that is disinfected with chlorine has .5 to 1ppm of chlorine. The EPA allows for up to 4ppm. This doesn't mean its going to be ideal for your hydroponic system. Read below.

    Jiji, how did you become an expert on sterile hydroponics?

    I'm not, and don't claim to be. Most of this info is just ripped off the net, I'll try to cite my sources. I'm just trying to gather facts and disseminate information to the hydro community.

    How a sterile res works with chlorine as an oxidizer

    Microbes are surrounded by a cell membrane surrounded by structural proteins. These proteins maintain their shape. When a strong oxidizer is present such as chlorine, proteins are released and they are accepted by the oxidizer. When the cell loses its proteins it loses its structure and disintegrates.

    The higher the ORP (oxidization Reduction Potential) the faster proteins are lost from cells.

    When you add chlorine in the water, thats called the Total Chlorine. Some of the Chlorine will bind with dirt, debris, plant etc., this is called Combined Chlorine. Combined chlorine is chlorine that is lost for disinfection. The rest is called FREE CHLORINE. Free Chlorine is in two forms, HOCL (Hypochlourus acid) and -OCL (Hypochlorite ion). HOCL is the only form that is active for oxidation. HOCL and -OCL change in proportion dependant on PH. Free Chlorine is about 95% HOCL at a PH of 6.5 and almost a 100% at PH 6.0. HOCL can generally easily be measured using a redox/orp meter.

    To know the disinfection properties, you need to know the ORP. ORP is measured in mV. Different oxidizers have different strengths. For chlorine a general accepted ORP value in hydroponics is 600mV to 750mV. This can vary on biological load, but probably closer to 600mV is better as achieving 750mV or above requires a fair amount of chlorine.

    I use calcium hypochlorite, in the form of pool shock. Its extremely cheap and easy to find. I make a liquid batch so that 1 ml when added to a gallon of water will equal 1 ppm chlorine. Dose as necessary usually every two days.

    Further reading and sources:
    --------------------------------------------------------------------------------------------------------------------------------------------- - UConn results.pdf

    bradburry Well-Known Member

    so its the pool shock i need at 1ppm......right?............good read btw :)

    bradburry Well-Known Member

    i got it on ebay thanks jiji

    SeedHo Well-Known Member

    here are few to add to your faq, after reading this, these were the questions i had, with going to links.
    how would a sterile res help me?
    what are the benefits vs cost?
    what kind of temps are needed and will temp effect the the oxidation process?
    if ya don`t know you have to ask.

    Thundercat Well-Known Member

    I've been using a pool shock solution for the last 1.5 years now. Its been working great. I was hesitant to try it at first, but its been the most cost effective solution to a sterile res. I spent $9 on powdered pool shock and have not even used 1/4 of the container since I started. I mix 1/2 tsp of shock powder with 1 gallon of water and shake. Then I add that solution to my res at 1 ounce of solution per gallon in the res about every 3-4 days. Just thought I'd share my experience.

    bradburry Well-Known Member

    oxygen dissolves best in colder water and even down to just above freezing .....i think .lol

    thats all i know ...
    SeedHo likes this.

    bradburry Well-Known Member

    where do you get your pool shock from and is the granules the same as powder?

    Thundercat Well-Known Member

    I bought it at walmart :). Granules is prolly what this is.

    bradburry Well-Known Member

    bloody dont they sell

    jijiandfarmgang Well-Known Member

    FAQ's Continued

    How would a sterile res help me?

    If you've had root rot/pathogen problems in the past, and have tried to circumvent them, but still seem to get them running a sterile res may resolve the issue.

    What are the benefits vs cost?

    The potential benefits from using a sterile hydroponic solution could be that it solves or mitigates your root rot/pathogen problem. The cost for a 1lb bag of calcium hypochlorite is 3-10 dollars, available locally at pool supply\box stores and treats thousands of gallons.

    What kind of temps are needed and will temp effect the the oxidation process?

    Temperature wont affect the oxidation rate of micro flora in a hydroponics solution (if it does, I could find no evidence of it). BUT higher temps equal higher biological load and will require more oxidation for sterilization. It is widely accepted that you shouldn't operate your reservoir temperature over 72f for DO/anaerobic bacteria, micro flora purposes. Probably ideally 65f-70f. Dissolved Oxygen increases as temperature decreases, and biological load increases as temp increases. It is feasible that having a hydroponics solution even colder than 65f may be beneficial, but at what temps does it start to severely inhibit plant growth I just don't know.

    Can you guarantee that if I follow these guidelines I won't have a pathogen/root-rot problem?

    Absolutely not.

    I heard Chlorine is a harmful corrosive chemical I'm going to stay away from it.

    I'm not forcing anyone, or not so much directly recommending that you use chlorine, or even a sterile res. I'm suggesting that you keep an open mind and make a logical decision on what will potentially work best for you.

    When handling calcium hypocholorite proper PPE (personal protective equipment) should be utilized. The recommended strength of chlorine in a hydroponics solution is similar to most municipal tap waters which has been used for over 100 years and has saved countless lives.

    Why not use UV (Ultra Violet Light) instead for a sterile res, it seems to work great for reefers.

    While it may be great for fish tanks and water treatment it may not be so great for hydroponics. The cost is higher to operate (initial investment and electricity) and certain micro nutrients can break down and or fall out of solution. It is used in some commercial hydroponic agriculture but definitive scientific information is hard to come by. UV, ozone, iodine, chlorine and other oxidizers all have one thing in common; none are infallible for 100% across the board solving a root rot/pathogen problem.

    I have some calcium hypochlorite (pool shock) that says 49% available chlorine. How much do I add to get 2 ppm of chlorine to a 100 gallon reservoir?

    To figure for 2 ppm of TOTAL chlorine is simple.

    Remember 1mg/L = 1 ppm

    So 2 ppm would be 2 mg per liter of water.

    100 gallons = 378.5 liters. So 378.5 x 2 = 757 mg

    But its only 49 percent strong. So 757/.49=1545 mg or 1.545 g

    - Jiji
    Last edited: Nov 2, 2014

    bradburry Well-Known Member

    im converted

    what do u mean by 1 ounce?.....sorry im

    Aeroknow Well-Known Member

    I would imagine: fluid ounce

    1 Fluid Ounces (US) = 29.5735 Milliliters
    jensen71, Thundercat and bradburry like this.

    SeedHo Well-Known Member

    jiji thank you.

    bradburry Well-Known Member

    i read somewhere that tap water can have upto 1ppm of chlorine and plants can uptake 1ppm of chlorine?..... So how much does my pool shock need to be in my res?
    Heavy Consumer

    Heavy Consumer Well-Known Member

    Thank you Jiji. If even I was able to understand this info, it must have been well presented! Very informative.

    TO what degree, if any, might the benefits of running a sterile reservoir vary between the different hydroponic growing methods (DWC, E+F, Aeroponics, NFT)?? Would I be right in imagining that with roots in water 24/7 (DWC), the risks of root issues are greater and thus running sterile might be more advisable (arguably)? Please excuse my ignorance. :oops:
    In your opinion, is it still a worthwhile practice regardless of method?
    jijiandfarmgang likes this.

    jijiandfarmgang Well-Known Member

    It seems DWC has the most issues. I don't know if it benefits so much...It's a kind of you need it or you don't thing (with any type of hydroponics) and your more likely to need it with DWC.

    I do think its a worthwhile practice regardless of method. However in EBB and Flow your less likely to need it.

    - Jiji
    Heavy Consumer likes this.
    Heavy Consumer

    Heavy Consumer Well-Known Member

    Thank you.

    bradburry Well-Known Member

    easily understood thanks jiji :)
    your on my list of people to believe .lol.

    ttystikk Well-Known Member

    My own RDWC experience was very, very clear; until I began to refrigerate my nutrient water and maintain its temperature in at least the mid sixties, nothing, but nothing stopped the rot. Not regen-a-root, not Dutch Master Zone, not even bleach. Plants grew like Crap or not at all.

    Once I installed my chiller and got the water temps down, I never, ever had a problem again, and I haven't used root conditioner/sterilant since.

    I've even gone to the extreme of putting in water I know to be bad and full of pathogens... only to watch my system clean the water instead of infecting the roots.

    Two things contribute; one, cold water, supplied by a chiller. The water must drop below 70, preferably 66 f every night at least once. Two is my replacement of airstones with waterfalls. I'm not sure how it helps, but it does. The grinding drone of airpumps is a noise I don't miss. The little gurgling noise of a bunch of waterfalls is much more pleasing to the ear- and the mood.
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    bradburry Well-Known Member

    i have my chiller at 16°c......does that sound ok?
    ttystikk likes this.

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