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Thread: PH difference

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    Junior Member Rank = Fry piscesman's Avatar
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    PH difference

    Hello
    I have a koi pond , the ph is reading as 10.5......I also have a separate tank with small koi in with a ph of 7.2
    I fill them with exactly the same water do water changes etc.. and cannot figure out why the difference any ideas please ?



  2. #2
    All the biological processes that take place in a pond tend to reduce the pH so the pond pH should never be higher than the tap water pH (after dechlorination and aerating overnight) unless this is due to a deliberate addition such as sodium bicarbonate or clay etc. If the pH is higher and there have not been any deliberate additions to raise it then something is leaching into the water.

    So, the correct way to approach this is to find the reason for the high pH rather than playing around having to continually add acidic treatments to cover an inherent problem of a continually rising pH.

    Initial question to ask is:
    What is your supply pH after it has been dechlorinated and aerated overnight?

    If the supply pH is higher than the usual pond pH then the next question to answer is:
    Have you increased the aeration?

    If the supply pH is lower than the current pond pH then the next questions to answer are:
    Do you use clay?
    Is there a large area of untreated concrete or cement?
    Are there limestone rocks in the system?

    If you can answer the initial questions, it will be easier to advise you on what you should do next.

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    ph reply

    Quote Originally Posted by Manky Sanke View Post
    All the biological processes that take place in a pond tend to reduce the pH so the pond pH should never be higher than the tap water pH (after dechlorination and aerating overnight) unless this is due to a deliberate addition such as sodium bicarbonate or clay etc. If the pH is higher and there have not been any deliberate additions to raise it then something is leaching into the water.

    So, the correct way to approach this is to find the reason for the high pH rather than playing around having to continually add acidic treatments to cover an inherent problem of a continually rising pH.

    Initial question to ask is:
    What is your supply pH after it has been dechlorinated and aerated overnight?

    If the supply pH is higher than the usual pond pH then the next question to answer is:
    Have you increased the aeration?

    If the supply pH is lower than the current pond pH then the next questions to answer are:
    Do you use clay?
    Is there a large area of untreated concrete or cement?
    Are there limestone rocks in the system?

    If you can answer the initial questions, it will be easier to advise you on what you should do next.
    thank you for your reply
    the ph supply is 7.2 .. the pond is reading as 10.17 this morning.. i do not use clay... there is no untreated concrete or cement areas.. and there is no limestone rocks in my pond.. am still at a loss.. Thank you..

  5. #4
    Quote Originally Posted by piscesman View Post
    thank you for your reply
    the ph supply is 7.2 .. the pond is reading as 10.17 this morning.. i do not use clay... there is no untreated concrete or cement areas.. and there is no limestone rocks in my pond.. am still at a loss.. Thank you..
    There may be a small increase in the pH of the supply when the water is first put into a pond but it's very strange to have an increase of almost three points on the pH scale unless something is driving up the alkalinity so here are a few more questions to help unpick what is happening:

    How are you measuring the pH; test kit or meter?

    Was the supply pH measured after it had been dechlorinated and aerated for a few hours?

    Do you use sodium bicarbonate to buffer the pH?

    Do you have any pH raising/buffering agents such as oyster shells or Canterbury Spar?

    What media do you have in the biofilter?

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    ph problem

    Quote Originally Posted by Manky Sanke View Post
    There may be a small increase in the pH of the supply when the water is first put into a pond but it's very strange to have an increase of almost three points on the pH scale unless something is driving up the alkalinity so here are a few more questions to help unpick what is happening:

    How are you measuring the pH; test kit or meter? both

    Was the supply pH measured after it had been dechlorinated and aerated for a few hours? no

    Do you use sodium bicarbonate to buffer the pH? no

    Do you have any pH raising/buffering agents such as oyster shells or Canterbury Spar? no

    What media do you have in the biofilter?
    plastic round balls with rubberized pipe to supply air.. also pond floss and blue green and black filter sponges with a stainless steel sieve for catching big items..

    the ph was normal then suddendly shot up after koi spawned have done 60 percent water change over a period of six weeks gradually... Removed spawn with spawning brushes. the ph has been gradually increasing . thank you
    Last edited by piscesman; 08-07-2024 at 07:19 PM.

  7. #6
    The pH of a pond is subjected to a lowering effect of the bugs in the biofilter so it won't rise significantly above that of the supply unless something is adding alkalinity. What are you measuring the pH with, was the supply pH measured after it had been dechlorinated and aerated and have you used sodium bicarbonate or are there any other buffers such as oyster shells?

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    ph difference

    Quote Originally Posted by Manky Sanke View Post
    The pH of a pond is subjected to a lowering effect of the bugs in the biofilter so it won't rise significantly above that of the supply unless something is adding alkalinity. What are you measuring the pH with, was the supply pH measured after it had been dechlorinated and aerated and have you used sodium bicarbonate or are there any other buffers such as oyster shells?
    Hi no other buffers.. but i am wondering if when i power washed algae growth off of fibre glass waterfall trays it revealed some of the fibre glass material under the coating.. do you think this could be the cause of the increased ph. please ?.. thank you..

  10. #8
    Quote Originally Posted by piscesman View Post
    Hi no other buffers.. but i am wondering if when i power washed algae growth off of fibre glass waterfall trays it revealed some of the fibre glass material under the coating.. do you think this could be the cause of the increased ph. please ?.. thank you..
    Please excuse the delay. Students seem to gang up - none for ages then several come along at once so teaching them sometimes sucks up all my free time.

    I doubt that exposed fibreglass resin or matting would affect the pH. A breach in a pond's fibreglass would only affect the pH if it went all the way through to the concrete blocks used to build the pool or, in your case any alkaline material used to build the waterfall.

    What are you using to measure the pH - test kit or electronic meter?

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    Quote Originally Posted by Manky Sanke View Post
    Please excuse the delay. Students seem to gang up - none for ages then several come along at once so teaching them sometimes sucks up all my free time.

    I doubt that exposed fibreglass resin or matting would affect the pH. A breach in a pond's fibreglass would only affect the pH if it went all the way through to the concrete blocks used to build the pool or, in your case any alkaline material used to build the waterfall.

    What are you using to measure the pH - test kit or electronic meter?

    Thank you for your help and replies i use a meter which is calibrated and i use a separete test kit ..

  12. #10
    All the biological processes in a koi pond tend to reduce the pH so the pH will only be lower than the supply unless you add something to raise it or there is alkalinity leaching into it and we've ruled that out. I keep thinking about this but nothing seems to add up to give me a starting point to determine why your pond pH is much higher than the supply pH without asking you to do more elaborate tests. So one thing I need to check before that is did you dechlorinate the supply water and aerate it overnight in a bucket before you measured the pH?

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    Whenever I’ve had the pH go up in my pond it’s been because of algae - it’s worth measuring the pH at different times of day to see if it is swinging.
    if it’s high during the day and lowers during the night, then algae photosynthesis could be reducing CO2 in the daytime which is acidic.

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