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pH spikes massively in small 4.5 gallon DWC hydro reservoir

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    HELP! pH spikes massively in small 4.5 gallon DWC hydro reservoir

    Hi - and first thing thanks to the owners for an absolutely awesome helpful website!
    It is so interesting as a new grower that I've literally read almost everything on here.

    So - just recently, growing and personal use of cannabis in private had been decriminalized in South Africa (yeah!) and I've set up my first small Deep Water Culture system after a lot of research.

    Everything is going well in the 4th week of growth after germination. EXCEPT for one major problem I cannot get around - huge pH spikes even when I check and ph-Down it twice a day. This is a big concern to me and one plant already showed pH-stress symptoms (I culled it and kept the other 5 who seem more resistant and therefore the stronger genetics theoretically).

    My local hydroponics shop all seem to agree that pH spikes a lot more in small reservoirs.
    I am just amazed that it spikes this much. Due to space constraints I cannot have a larger reservoir.

    I would lower pH to around 5.5 and within 10 hours it is well above 8 to 8.5 pH (using calibrated pH pen)

    I use a strong pH down (first started with weaker acetic acids and now on the proper strong phosphoric which stabilizes it slightly longer).

    The spikes occur no matter whether the water and nutrient mix is fresh or 5 days old.

    Reservoir 17 liters water (4.5 gallons) just under the net pots but not touching.
    Very good liquid nutrients at correct rates for growth stage.

    5 small plants (4th week) with no roots in water yet.

    Combined with a wick-system - wicks are hemp twine (best absorption height and rate after experiments with at least 8 materials)
    Note: This is the ONLY organic component directly touching the water in the reservoir.

    A garden stone weighing down the air pipes and air stones of my air pump (Garden stone was cleaned and sterilized with vinegar and sealed in a Ziplock bag)

    No algae growth or light entering.
    Fans for circulation.

    High dry temperatures - 32C - 90F but local bagseed strains should be adapted to climate.
    Bagseed because this is still experimental and legal purchase of seed still has no clear legislation on.

    CFL lights.

    I really just simply wish to know whether large spikes in small reservoirs and high temperatures are common and if there are solutions to this to at least minimize it. And I understand fully that different growers have different views and opinions and I would gratefully consider/weigh all of them.

    Please ask if you need more info.

    Also note due to electricity costs in my country, I cannot for the moment afford fancier equipment such as extractors, water drip pumps or humidifiers. So I am sticking to the basics for now.

    Howdy MaxHeadroom1970, I have been growing with hydro (6 gal. Bubbleponics X 2) for eight grows now. I use the local tap water (mix of well and lake water)with a high mineral content. The pH should fluctuate some as the nutrients are taken up by the plants, and different nutrients are absorbed better at different pH levels, so some fluctuation is necessary for proper plant growth. I keep the air temperature around 70°F and 85°F, the reservoir water temperature between 60°F and 70°F.
    I would recommend getting some pH test strips to double check the pH meter's reading, the pens can get out of adjustment with regular use. I have not had any good experience with the pH pens and use a dual panel test strip (range 4.5 to 9.0) made for testing the body's pH. I never try to adjust the pH in the reservoir, I start off with the nutrient mix at 6.0 and adjust the pH of the fill or top off water at the mid week. I nearly killed my plants during one grow by trying to keep to control the pH too closely.
    Smoke weed,.....grow peace!


      Hey DW2 - thanks for your quick response. Everything noted.

      The pen is brand new and I use "7" calibration fluid every time. We also tested it at the store.

      The idea of tests strips as back-up is a great one and I will do this.

      Our tap water pH is around 7 to 7.3 before any adjustments or nutrients- this too shows the pen should be accurate.

      I still have to do a temperature reading of the water and will do so as soon as I have a thermometer for the purpose.

      I also adjust and stabilize pH of any top-fill water before adding. And currently replace the entire reservoir and nutrients once every 6 days.

      Thanks again.

      Do you also get quite big spikes in pH in your smaller reservoir?


      • DW2
        DW2 commented
        Editing a comment
        The only time that I had large changes in the pH, was when I was 'messing' with it too often. I now only check and adjust when I feed and check the reservoir pH at the mid week top off. At the top off, I SWAG the pH level of the top off water to approximate an acceptable level in the reservoir. I have read where variations in the pH level allows the plants to better absorb the different nutrients. I have found that 'chasing' the pH level can be detrimental to, not only the plants, but to the grower as well, Who needs extra stress these days.

      In a 5 gallon bucket... with 2-3 gallons of water in it... I ph down twice per week.
      Sounds like you are missing very important PH buffers. Which can cause swings like that.
      Last thing to consider, is this new hydroponic equipment you are using? If so, PH swings can be a factor in new equipment. If that is the case, just keep adding those buffers and dealing with the swing. In time the new equipment will stabilize and the PH drift will be less drastic.
      4x4 600w HID empty for summer
      3x3 400w HID with Bruce Banner and Skywalker Kush
      2x2 65w Quantum Board LED with 4 mother strains
      running all simultaneously for a perpetual harvests.


        Hi Toker1 - and thanks.

        I admittedly had to do some reading on buffers. Man, this is seriously scientific stuff and another reason I love it.

        Yes all the equipment is brand new - in fact I did consider that all the new plastic surroundings should probably have some effect on the water. That is also why I mentioned the stone and the organic wicks which might affect it. It makes sense that in time the new plastics should stabilize .

        I will read up more on buffers. (PS: I actually tried some citric and acetic acid but they were too weak and stick to phosphoric now)


        • MaxHeadroom1970
          MaxHeadroom1970 commented
          Editing a comment
          Thanks again and I agree. Did a water change today and the pH definitely already stabilized more since this thread started. I still have to do EC tests but I think the plastic played a role.

        • Toker1
          Toker1 commented
          Editing a comment
          Yes, I agree. Every new system seems to have a PH swing when first used. Then it tends to stabalize out after some time. I believe that plastics are not inert. They either absorb or release free ions which affect the hydrogen concentration and cause the PH swings. After this is depleted, and there are no more free ions to give up (or the bonds have already been forged with the plastics)...then the solution will stabalize PH.

        • MaxHeadroom1970
          MaxHeadroom1970 commented
          Editing a comment
          I believe we had found the solution to my extreme pH fluctuations. Especially since I did everything according to the book. I've changed the water and nutrients recently and it is very stable compared to previous changes. So - in my case it seems that the new plastics take around 3 to 4 weeks to stabilize and to not severely affect the pH.

          But I think the conclusion is that new plastics in systems can quite badly affect pH but seems to stabilize after around a month. Solution being to choose the plastic wisely when starting off. Thanks.

        So I recommend you get another type of pen to test EC it measures the amount of electricity can pass through your water and how easily, plants use this same system to intake proper amounts of water and nutes alternatively. Like Toker suggests your water may not have enough salts in it to help stabilize PH, EC can help you see how high your conductable salt level is. Start taking daily tests and you should start to see that you might have a very low EC
        Grow and good luck
        Current grow:

        past grows:


        • MaxHeadroom1970
          MaxHeadroom1970 commented
          Editing a comment
          Thanks. I haven't done EC tests yet, so it seems that will be quite important.

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