So as I reviewed my past KHA articles I noticed that I had not written anything about pH and as I’ve had several discussions during this spring’s pond visits we’ve talked about and dealt with a couple pH issues in local koi ponds. I will set out to keep it simple and not go too deeply into the chemistry side but some basic concepts are needed to better understand what’s going on in your pond water and how it affects your koi. Before I start to lose readers, I want to start with an important recommendation that you not get caught up in any effort to be constantly buffering your pond water to achieve and maintain the established ideal pH range for koi of 7 to 7.5. And that’s so true for those of us in southern California with the average pH for local water districts having a pH of 7.8 to 8.2. It’s just less stress on your koi to simply adjust to local water pH than to be dealing with larger daily swings in pH due to buffering chemicals to reduce local pH levels.
Now to the science stuff – I’ll skip the chemistry jargon and go with simply that a pH reading is a ratio of the base component to the acid component and when they are equal in amounts the pH will be neutral and measured at a value of 7. pH values greater than 7 are base positive and values less than 7 are acid positive. Sorry, I just can’t help myself – Why? – If you have more hydrogen ions (H+) in your water it will be acidic and if you have more hydroxyl ions (OH-) your water is more basic. Finally, the pH reading is logarithmic so a change in reading of just 0.3 comes close to doubling the (H+) or (OH-) activity and a change in value of 1 is a 10 fold change in (H+) or (OH-). That’s the simple reason why pH changes need to be made slowly! Done with the science – not too bad.
So let’s move on to pH and your koi. Generally speaking koi can live and survive a pH range of 5.5 to 6 and from 9.5 to 10 depending which author you read but all generally agree that 7 to 7.5 is optimum for koi physiology, and they can readily handle pH changes when done slowly. Again depending on which author you are reading the daily swing in pH reading should not exceed 0.3 to 0.5 or your koi will experience pH change stress. How so? (back to the science) – First just know that the blood within your koi has a pH value and the pond pH affects koi blood pH chemistry. When pond pH is and remains high the pH of your koi’s blood starts to suffer from alkalosis and koi losses are not uncommon or reduced life span due to continuous pH stress. You will feel excess slime coat and staying at the surface (gulping/pipping for air). For the reverse, an extended period of low pH leads to a condition called acidosis within your koi’s blood system pH; values will again create excess slime but koi become anorexic and will rest on the bottom of your pond and get red streaking lines in the fins which can lead to koi losses and/or reduce life span. Why? - Our koi are NOT water tight as water is constantly entering the fish and if this water is low in pH then the koi has to use its own natural internal buffers to raise the blood pH and they are quickly consumed leading to low blood pH or acidosis.
Special Note: As our pond is a system, when I’m called about a high or most often a low pH reading in a pond – My first questions are almost always “What is the ammonia reading and the KH or alkalinity reading.” For a low pH reading a condition called pH crash is well documented in articles concerning this subject and to just raise the pH by adding baking soda (calcium carbonate) you can inadvertently have higher fish loss due to ammonia poisoning as pH contributes to the toxicity of ammonia. Just a little science – at a pH of 7.2 or lower the ammonia is mostly ionized (NH4) and less toxic to the koi, but as the pH rises the NH4 converts back to NH3 unionized and is more toxic to the koi as it now can pass back into the koi through the gills and other exposed tissue. And in warmer water the conversion rate is increased – it’s a system. Got your thinking cap on - the conversion from NH4 to NH3 frees up a hydrogen ion and yes they will have a further reducing effect on pond pH.
You should have a way to measure your pond pH – dip sticks with a color chart or electronic pH meters. For dip sticks quickly reseal the lid after removal and buy new ones if older than a year. For pH meters – store upright with the probe always in storage solution and don’t let it dry out!!! Follow manufacturer directions closely for probe calibration and cleaning and change probe every couple years. Store both in cool dry area!!! Your pH will be lowest in early AM and can be expected to rise throughout the day, so early AM, maybe noon, and just before dark to get a reading of your pond’s daily swings. For established ponds you could go to weekly readings, and I like the day before and after my weekly big water changes to record effects of water changes. Yes, this info needs to go in your pond journal!!!
So what affects your daily pH changes? First, hard water (southern California) is more basic and resists changes to pH and soft water is more acidic and changes quicker. Little science – pH is reduced by oxygen consumption, production of carbon dioxide (big time), filter activity (nitrogen cycle), and decomposing waste in the pond. Why’s? – 1. Hard water has more buffering capabilities as it has a higher alkalinity (more dissolved mineral anions as in carbonates CO3, bicarbonate HCO3 and hydroxide OH-) 2. Carbon dioxide converts to carbonic acid (pH down). 3. Nitrogen cycle produces or frees up hydrogen ions (pH down). It also requires and uses the available alkalinity, as in calcium carbonate, which further reduces the pH. Note: If you have a lot of plants in your pond then the carbon dioxide produced after dark will further reduce your pH during the night. Of course the reverse is true after daybreak as all the green stuff in your pond is now consuming the carbon dioxide and producing oxygen – thus the rise in pH.
When treating pH issues, high pH is usually treated by dilution in the form of water changes with water of a lower pH value. Lower pH is usually treated the same way but with water with a higher pH and baking soda (calcium carbonate) is used to keep your alkalinity to between 80 and 120 parts per million (remember the filter uses it up during the nitrogen cycle). Repeat: Use caution when raising pH and always deal with any existing ammonia by first using an ammonia binder such as ClorAm-X, Prime, Ultimate, etc.
I’ll end with a repeat of my first recommendation – Please do not chase or try to maintain a pH of 7 to 7.5 with daily chemical additions to pond water causing large pH fluctuations and unwanted stress for your koi. Koi will and do adapt to say a pH of 8.2 – especially when the daily fluctuation is kept at 0.3 to 0.5. Disclaimer – There are water quality monitoring systems that work 24/7 to maintain certain water parameters of which pH is one and if you got the $$$ -they work, and at a lesser cost but still pricey a water softener system in front of a reverse osmosis system keeps my pH at 7.3 to 7.5, with a 50 percent R/O water waste down the drain and the other half to the pond. My water bill is $525 to $575 per month.
My goal was to introduce the basic important issues concerning the subject of koi pond pH, and this article only scratches the surface of the subject. I encourage you to refer to a web search on the subject or as usual read the articles/books written by D.V.M.’s Erik Johnson and Nicholas Saint-Erne. Our club website has Norm Meck’s water quality articles which also contain info on this subject.