The Perfect PH For Your Koi Pond

What PH should my pond be?

If ‘How often should I change my water?’ is our most frequently asked question when speaking to customers, the second most asked is about pH.  It is easy to understand why PH causes so much confusion though, with lots of mis-information out there.  Hopefully this guide will clear up most questions you have about PH.

What is pH?

pH is a figure expressing the acidity or alkalinity of water.  It is a 0-14 scale; one is the most acidic and fourteen is the most alkaline.  A pH of 7 is classed as neutral. It is important to note that the difference between one pH reading and the next level up is ten times, not one.  For example, a pH of 9 is ten times more alkaline than a pH of 8, and 100 times more alkaline than a pH of 7 (10 times 10).

Many people will disregard a pH climb of 1.0 on the scale as insignificant, but to give you an idea it is the difference between a temperature of 10 degrees Celsius and 20 degrees Celsius – a big jump!

Tap water

Invariably, 99% of the water in your pond comes from your tap.  Tap water can vary in pH depending where in the US you live.  When a pond is first filled up, it will carry an identical pH reading as the tap water for a short while.  As the pond starts to mature, after a month or so, the pH will change; usually rising slightly.  At this new level, the pH will settle and you will get little fluctuation in readings should everything be going well with your pond.

In an ideal world, your pH would read between 7 and 7.5 all of the time, but if this cannot be achieved don’t panic too much.  Consistency is more important in recording pH levels.  For instance, customers in South may have a tap water pH of 6.8 and an established pond pH of 7.2.  It’s good as long as it is consistent. Areas in the North with hard tap water can have reading as low as 6.5, and again this will not be too detrimental as long as the water is consistent in pH throughout the year.

pH buffers

There are several treatments on the market that you can buy to buffer pH up or down, but we would suggest to stay away from these as it can cause more harm than good if you get it wrong.  They are also drastically overpriced.

The best and only pH buffer you will need is Sodium Bicarbonate AKA Baking Soda.  The addition of Baking Soda to your pond will increase your KH levels which will stabilize pH levels, keeping them from fluctuating. We have previously already covered testing KH Here.

pH Terminology

pH swings: As mentioned earlier in the article, there is a huge difference in just a 1.0 movement on the pH scale.  If your pH moves more than five individual 0.1 increments in either direction in a short period of time, this is called a pH swing. This can only be measured with a digital pH meter, as general test kits will not be able to measure these ‘mini’ increments.

Ph Crash: A pH crash can occur in a small pond or on seventy acre lakes.  Too much rain or snow in the pond can lower the pH levels, but keeping an eye on your pH reading can give you a warning shot of anything that may be up.  Also, doing a five minute observation can help you see warning signs, such as your fish behaving strangely.


If your pond is healthy and your koi are happy, you don’t have any problems; your pH cannot be that bad.  Your Koi and pH reading will tell you if something is wrong, so don’t worry too much, or obsess over pH.

Definitely do

  • Use a pH meter if possible, its measurement is more accurate than a dip test kit; don’t buy the cheapest pH meter around, but you don’t need the the most expensive either.
  • Test & Buffer your KH in order to maintain a consistent PH level.
  • Test your pH at the same time each day, as they can fluctuate at different times of the day.
  • Consult an expert before adding buffer solutions of any type.

Definitely don’t

  • Allow too much rain water into the pond; if this does happen it can  affect the pH.  You can do small water changes regularly up to 10% until your pH returns normal levels .
  • Likewise, keep heavy snow fall out of the pond.  Clear any snow from pond covers or sheeting in the Winter.  Small amounts should be OK.
  • Don’t try to achieve the perfect 7.5 pH – if your Koi are happy with a pH of 7.2 or 7.8 then leave it as it is.  Otherwise, you can cause more harm than good.

And finally remember ph is all about consistency - achieving this will give you happy koi and a healthy pond!

We hope that has cleared any pH related questions you may have.  Feel free to comment below and ask any more questions, and please share this article if you found it useful! 

  • Apr 03, 2019
  • Category: News
  • Comments: 0
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