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  1. #1
    Junior Member Rank = Fry Billy M's Avatar
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    Diurnal pH swings

    Hi I have an 19k ltr pond set up last Sept 1.5m deep semi shaded and temp 12 all winter . Only six fish atm . NO2/NO3/NH3 all 0 since early Nov . PO4 0.25 KH 5,GH 5
    However I am seeing a big pH swing 8am 8.2 - 7pm 8.6/8.65.
    The cause seems to be heavy algae on the pond walls which I’m trying to brush off but it’s a never ending job.. I have plenty UV and a trickle
    anything I can use to buffer the increasing pH ?
    I’ve read I could use dilute white vinegar to keep the pH down but that’s treating the symptoms not the cause !
    fush are all really happy at the moment but I want to solve it before they aren't !
    any advice please



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  3. #2
    Hi Billy, I have exactly the same issue and would be interested to know ow if this should be added to my list of things to worry about or if it's okay. I've read that trying to bring down your PH with acid can hammer your KH leaving the pond vulnerable to a crash.

    Sent from my SM-G986B using Tapatalk

  4. #3
    Senior Member Rank = Supreme Champion davethefish1's Avatar
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    most new ponds start with a higher ph, mine was at around 8.2 with swings during the day when first set up.
    your filters may have cycled, with nitrosomonas and nitrobacter.
    but they take longer to fully mature and create a diverse eco system...

    now mines matured it's steady at 7.6 and the swings are very small, especially since building a pergola..

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  6. #4
    Photosynthesis removes dissolved CO2 so many people blame it for causing pH variations but the correct way to look at photosynthesis is to consider that it doesn't cause the variations, it restores your pH to its normal value after CO2 from fish respiration has lowered it during the night. That may seem odd but this explanation might make pH variations easier to understand:

    Measure your pH at the end a sunny day when photosynthesis has removed as much of the dissolved CO2 as possible and call that your natural pond pH. Measure it again as early as possible in the morning and the difference between the two is caused by dissolved CO2 due to fish respiration.

    If there were no fish in the pond there would be no downward night time change, due to dissolved CO2, for photosynthesis to restore or, if you suddenly added a load of fish without altering the aeration, the night time reduction in pH due to the increase in dissolved CO2 would be greater. So, photosynthesis should be seen as helping to restore the natural pH by removing the variable parameter (dissolved CO2) that lowers pH rather than photosynthesis causing an upward variation.

    Koi can happily adjust to any pH in the range 7.0 to 8.5 but they have to make biological changes to keep their blood pH in a narrow range (7.7 to 8.0) regardless of the pond pH and the maximum pH variation they can cope with without becoming stressed is 0.2 per day.

    If you want to reduce the daily variation, first try greatly increasing aeration to gas off the excess CO2 and, if that doesn't reduce it enough, you will have to increase the KH with a possible increase in pH.

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  8. #5
    Senior Member Rank = Supreme Champion Ajm's Avatar
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    Quote Originally Posted by Manky Sanke View Post
    Photosynthesis removes dissolved CO2 so many people blame it for causing pH variations but the correct way to look at photosynthesis is to consider that it doesn't cause the variations, it restores your pH to its normal value after CO2 from fish respiration has lowered it during the night. That may seem odd but this explanation might make pH variations easier to understand:

    Measure your pH at the end a sunny day when photosynthesis has removed as much of the dissolved CO2 as possible and call that your natural pond pH. Measure it again as early as possible in the morning and the difference between the two is caused by dissolved CO2 due to fish respiration.

    If there were no fish in the pond there would be no downward night time change, due to dissolved CO2, for photosynthesis to restore or, if you suddenly added a load of fish without altering the aeration, the night time reduction in pH due to the increase in dissolved CO2 would be greater. So, photosynthesis should be seen as helping to restore the natural pH by removing the variable parameter (dissolved CO2) that lowers pH rather than photosynthesis causing an upward variation.

    Koi can happily adjust to any pH in the range 7.0 to 8.5 but they have to make biological changes to keep their blood pH in a narrow range (7.7 to 8.0) regardless of the pond pH and the maximum pH variation they can cope with without becoming stressed is 0.2 per day.

    If you want to reduce the daily variation, first try greatly increasing aeration to gas off the excess CO2 and, if that doesn't reduce it enough, you will have to increase the KH with a possible increase in pH.
    So would a shower help with this then as it gasses off though the tiers or am I miss understanding that one. Sorry if its a stupid question just adding up every pro con to a shower as I really want one

    Sent from my F5121 using Tapatalk
    Freddyboy the legend

    "we are water keepers first"

    Johnathan

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  10. #6
    That isn't a stupid question Johnathan and the simple answer is yes.

    Many people blame the showers they've just installed for the sudden rise in pH that occurs but, in reality, it's just because their total aeration has increased and the excess CO2 is being gassed off which results in a higher, but more stable pH. You can buy a shower to increase your aeration or you could get the same result with a more powerful air pump and a couple of extra airstones

    If it helps with your decision as to whether to buy a shower, you can tell your financial controller that you need the extra aeration the shower will bring to gas off excess carbon dioxide and stabilise the pH for the health and wellbeing of the fish. That should sound technical enough but you can elaborate if you wish. Of course that would mean that you would then live in fear of retribution if they ever found out that a few extra air stones would have achieved the same result

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  12. #7
    Moderator Rank = Supreme Champion Feline's Avatar
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    Giving the pond some shade in the afternoon is another way of limiting pH swings. I personally think it’s a better option than raising the KH further, when I tried that in a previous pond I found the pH went over 8.5 in the afternoon ‘early evening and the fish were very unhappy about it. I put a shade sail over that pond which fixed the swings completely. My current pond is in sun, but the larger volume seems to help with stability.

    The other thing you can consider is having an extra air pump on a timer to come on overnight when the pH is at its lowest, because that gasses off CO2 and raises the pH at the lowest point in the swing.

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  14. #8
    Senior Member Rank = Rokusai JimJones's Avatar
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    " Financial controller "

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  16. #9
    Junior Member Rank = Fry Billy M's Avatar
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    Thanks for the comments . I’m aware there is also significant CO2 from the algae overnight which I believe is the key issue as I have a spindrifter airway ion in the pond & aeration in the drum .
    my main issue is how to buffer the top end down - I’m lookingi to increase the Calcium with small amounts of CaCl but if I can remove the algae i think it should also help reduce the swings .Other than physical removal is it wise to add the various commercial treatments available to address the algae growth and what are the chemicals actually in them ?

  17. #10
    In an averagely stocked pond, the greatest contribution to dissolved CO2 at night is fish respiration. Obviously, the contribution that algae makes would be eliminated if you could remove it all but, if you have a CO2 build up during the night, it means that your aeration isn't as high as it should be. The easy way to remove dissolved CO2, whether it has come from algae or fish, is to increase the aeration which would have the benefit of increasing the level of dissolved oxygen in the day as well as at night. If you just remove the algae without increasing the aeration, you will lose the reduction it makes to CO2 during the day and you will have a permanently high dissolved CO2.

    It's possible to lower the pH by acidic chemicals but the ideal pH of a pond should be close to that of the source water, after it has been dechlorinated and aerated. If it isn't, every time you do a water change, you will have a step change in the pH which will cause stress unless you readjust it fairly quickly to the value you've chosen.

    If your supply water pH is high, the way to permanently lower the pH of the pond without the risk of stressing the fish when you change water is to use RO and adjust the mix of RO water and dechlorinated supply water to the desired pH.

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