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Pond water Ph

Our pond is now 4 - 5 years old, quite deep and partially in sunshine.  Ever since the first test our pond water has had a high Ph reading.  It should be around 7 - 8 but is 10!  We have tried all sorts of things but nothing has lowered the reading.  Is there a product on the market that we can use to lower the reading.  We do have newts in the pond, but only water lilies and blanket weed seem to grow, most other plants have died off.


  • LynLyn Posts: 21,868
    Has all the pond weed died off as well,   Hornwort and so on? 
    The top needs to be covered with plants for about two thirds. 
    Gardening on the wild, windy west side of Dartmoor. 

  • steephillsteephill Posts: 2,672
    10 is very alkakine indeed. How are you measuring pH? Cheap pH meters are notoriously inaccurate so I recommend cross-checking your readings with other instruments. You could try taking a sample to a fish shop (aquariums, not a chip shop!) and ask them to check it.
  • SkandiSkandi Posts: 1,673
    First you have to figure out where that reading is coming from 10 is high. what is the pond made out of, and what type of stone have you added to it, it sounds to me as if you have either a concrete pond, which it doesn't look like, or you have added a lot of limestone pebbles/rocks and those are keeping the pH up.
    You can buy products that will reduce the pH but you will need to constantly use them if either of the above is true.
    If all of your rocks are pretty neutral and there's no concrete I would do a partial water change and then add the product of your choice. Keep an eye on it for at least 6 months before adding any fish or any plants you care about.
  • Most of the plants that we initially bought did die off, but the lilies and blanket weed - oh and water cress seem to like the pond water and have done well.  We are using what is probably a cheap meter to gauge the Ph and perhaps we should try another or as you say steephill take a sample into an aquatic shop, although the fact that plants have died is a reason to believe our meter.  I would love to have more plants on the surface of the pond but this year I am wondering if it is worth buying more - just to see them dying off.
  • Butterfly66Butterfly66 Posts: 883
    I would get a second opinion in the pH reading and if possible an analysis of the water to try and establish what’s causing the high alkalinity. I don’t know enough about ponds but presumably a specialist aquatic nursery/shop could advise as already suggested.

    Having said that given that you have built the pond and it’s not connected to any other waterway/source then logically it must be the materials used and the stones would seem the most likely source? Do you know the product source and stone types - it may be worth rechecking that they were suitable for use on ponds and/or contacting the suppliers. limestone, concrete and some reconstituted stone can all effect the pH.

    When first getting into gardening, I watched in dismay as a previously healthy Acer slowly died. It didn’t occur to me at the time that it was the limestone stone mulch I had used (and was so pleased with) which was killing it off 🙄
     If you have a garden and a library, you have everything you need.”—Marcus Tullius Cicero
    East facing, top of a hill clay-loam, cultivated for centuries (7 years by me). Birmingham
  • Thank you all for your helpful comments.  Sorry that you lost an Acer Butterfly66, they are such lovely plants - it must have been heartbreaking to see it slowly dying.  The stone we used was granite and then there were the pebbles which I washed before laying on the liner to make a beach.  We do need to investigate further and will hopefully find an answer to this pH problem.
  • Pete.8Pete.8 Posts: 10,244
    How are you testing the pH GD?

    The plants in my wildlife pond are already growing well and I see plenty of snails and newts going about their daily business.
    I've just checked the pH and it's 9.1
    The pond is filled only with rainwater which here is usually around 6.5
    Knowledge is knowing that a tomato is a fruit.
    Wisdom is not putting it in a fruit salad.
  • Your water reading is interesting Pete.8. I am pleased and surprised that your pond plants are doing well.  We also have the ramshorn and normal snails too and newts, no frogs, it is just the plants that seem to dislike our water.  I will try again this year, but firstly we will have our water tested by a different water tester and perhaps pop along to the pond shop to see if they have any natural means of reducing the reading, although I have never heard of any such substance.
  • Pete.8Pete.8 Posts: 10,244
    There's still a big difference between 9.1 and 10.0
    Funny - I've never had frogs in my wildlife pond either - lots of newts though.

    One thing I wonder looking at your photo, there's a lot of soil? around your pond.
    Is rainwater running through the soil and draining into the pond?
    If so, that could account for it.

    The most successful plant in my pond by far is Brooklime-
    I found it really easy to grow right from the start
    It has also managed to self-seed itself into the garden borders too somehow...
    Knowledge is knowing that a tomato is a fruit.
    Wisdom is not putting it in a fruit salad.
  • So yesterday we took a sample of our pond water to the fish/pond shop. (No we don't have any fish in our pond.)  The pH reading was off their scale.  We purchased three packets of pH adjuster under the manufactured name of Blagdon which is the correct amount for our large pond. Mixed in with water and now hopefully bringing the Alkaline reading down.  We are hoping the wildlife will survive, if it safe enough for fish then hopefully it will be alright for our wildlife pond.  How long it lasts is the next thing.  
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