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So, which one is more important KH or pH?  Answers on a postcard please!!


In this article Stephen and Anthony Grey explore their findings in regards to how PH and KH play an important role in harmonising an ecosystem that can successfully rear nishikigoi. I found their thoughts very interesting and with permission, I collated their thoughts and so World of Nishikigoi proudly presents their ramblings...


Sitting in the garden (with our waterproofs on!) having a well-earned cuppa Anthony and I got discussing some recent posts regarding pH & KH and cast our minds back to 2003 when we nearly had a pH crash! Since then, it’s a subject we’ve always been interested in, more so these last few years…

It can be a mind boggling subject and took us a few years to grasp the fundamentals regarding what was going on with our water in relation to our bio filter - nitrification cycle, CO2 levels, TDS, GH and of course pH & KH. Back in 2003 information on these topics was limited, something we take for granted now.  Having previously kept and bred Malawi Cichlids successfully for many years, I already had an understanding of pH and the basics of the nitrification cycle but taking on a koi pond proved a whole different challenge!


Personally, I think every koi keeper should have a basic understanding regarding pH, KH and the nitrification cycle for the welfare of their koi. This is where the likes of BKKS, Koi clubs (koi shows) and dare I say it forums are a great help for newbies coming into the hobby.


We always trial & error whatever we have done over the years, so our experiences are exactly that, our own! We're simply trying to broaden our understanding and put the best practices we can into our hobby, take from our thoughts what you will. 


For us having very low alkalinity source water (low KH & pH) and using Nexus filtration (K1) as our main biological unit we used to try our best to stabilise the pH in our system, to stop large swings. Bags of oyster shells were deployed, suspended in the outer k1 chamber of our nexus. After so long these would just disintegrate, though at the time we did not fully understand why.  We would also put clay in the pond to try and help the skin, we mostly did well at koi shows, but we did struggle on occasion with the koi being veiny, again without any understanding of why. 



Eventually fitting a Bakki shower (2007) helped balance the alkalinity a little, by aiding gassing off CO2, etc. We are firm believers that fluidised K1 and BH Media complement each other! Well it works for us!

we did not really understand or even know about the likes of carbonic acid affecting KH and what was happening with the bio-filter.


Also, understanding that rainwater most times was off the acidic scale so counter measures were put in place by building a pergola to stabilize the effect the rain was having fluctuating our pH value.


Our pH would also swing higher throughout the day due to photosynthesis, and as carbonates were being consumed also affecting our KH, (as we started to understand more about KH realising this was happening). As it gets dark, dissolved oxygen (DO) levels lower and the photosynthesis stops and all plants (the algae on our pond walls) in our koi pond consume oxygen (respiration). So, in heavily stocked ponds (which we learnt to reduce as the years went on) CO2 concentrations can become high as a result of this respiration. The free CO2 released during this respiration reacts with our water and dissolves, producing carbonic acid so was lowering our pH value and KH during the night, early morning.  As we started to understand more about KH in relation to the nitrification cycle…counter measures were by introducing Plecos.


To control the swing, we would also add bicarbonate of soda (bicarb) mechanically by hand most evenings to combat the above. With little knowledge or experience at first regarding how much to dose, this was incurring too much of a swing and keeping our pH a little too high than we actually wanted based on the source water.  As time went by, we experimented with the daily amount of Bicarb to add until we could hold the pH as best as, without too much of a swing as we should not introduce our koi to a maximum swing more than 0.5 points within a day…ideally no more than 0.2. This swing can be stressful to our koi as the internal acid-base balance of our Koi changes as the pH of the water changes, also the toxicity of the ammonia in the blood stream changes as pH changes effecting vital organs…constant swings possibly cause of parasitic issues!


As said, testing at certain intervals during the day we realised we were putting too much bi-carb in thus keeping our pH too high based on our source water as this creates a bigger swing!!!!!!!!


We also noticed the change in the winter months when we were not feeding that we did not have to buffer so much in fact our pH was a little higher, which meant the KH was not being eaten up by carbonic acid. But when we started to cover our pond in the winter, we started to notice a difference again due to Co2 (pond not breathing) as mentioned in one of our previous Saturday threads…so that was another learning curve!!...counter measure was to build a polycarbonate framed cover to create more air space.


So those early years we eventually managed to get a handle on things even though we were sailing close to the wind at times. Our source water…THEN WAS…KH approximately 17mg/L to 25mg/L, pH approximately 7.1 to 7.2, TDS approximately 100. In fact, over the years there has been a slight change to where our approximate readings…NOW ARE…KH about 13mg/L, pH 6.90, and TDS about 80 from the tap!


NOW…this subject depends on your source water as there are so many variables in KH, GH making TDS and what your pH may be. It also depends on possibly where you want to be in the hobby. For “newbies” who are still learning and understand this subject…stability is the main reference by understanding to keep everything stable and safe, but obviously this is governed by your source water. Of course, certain parts of the country the source alkalinity is very high so therefore easier to maintain that stability, but as said as more of us are learning about Koi pond water chemistry and growing koi there is a desire to change the source water normally by other means such as RO. If your source water alkalinity is low’ish for stability and safety margins I would recommend certainly for newbies to keep if possible, their pH around 7.4 with a KH value in the region of 4°KH (72 mg/L), then from there if desired the KH and pH can be reduced once confident to do so. As said, the main requirement is to keep everything stable. (Alkalinity KH is measured in mg/L or degrees °KH. One degree KH = 17.8 mg/L.).


We now keep our pH at 7:00 and KH around 13mg/L based on our source water as our source water dictates this. To help us (as discussed on another Saturday thread) we have installed a pH Controller and Dosing Pump using an industrial Probe, this was about 5 years ago. The Dosing Pump wired into the pH Controlleris supplied from a 15ltr bucket that contains the Sodium Bi-carbonate solution going into one of our bio chambers. So, this effectively is taking out the mechanical guessing game (us), this is all automated based on our set variable point to maintain a stable pH of 7.00. By keeping our pH at 7.00 means we have very little swing which makes a big difference to the koi’s skin! Having an affective trickling in system backed up by a very good purification system (again a past Saturday thread) this buffers the alkalinity and tops up the carbonates for our KH to assist the nitrification cycle. Because we use our source water readings to dedicate our ponds pH and KH, means it reduces the need for constant dosing of Sodium Bi-Carbonate… so reduces fluctuations. So this is our counter measure for over dosing.


For about the first 5 - 10 years and doing ok on the show scene with our koi averaging size 4 (55cm) we noticed they never really grew or developed into the next size, which is partly down to genetics, but we started to put it down to our water not being exactly right. So about, seven years ago we started to change direction based on what we had previously learnt and put this experience into best practice. Starting by reducing the number of koi in our pond, re vamping our pond to aid directional flow, etc, fitted drum and upgraded our bio significantly (bio/Bakki chamber). We also upgraded our water purification and changed our water tricking in regime. Then basically started again with our koi, our main pond is just over 5000g and we currently only have 7 koi in there and since we understand to run our pH at 7.00 maintaining this value with no more than a climb variation of 0.2 value and along with a good trickling in / out and purification regime to top up the carbonates has made a huge difference in our koi’s growth rates and their overall health such as little parasitic issues.


Based on our feeding regime last year and feeding heavy backend of the summer into the autumn our biofilter(s) performed extremely well, with no ammonia NH3 readings indicating the ammonia oxidizing bacteria are present and performing their task in removing the ammonia that the fish are excreting and converting it and producing Nitrite NO2. With no NO2 readings means the nitrite to nitrate bacterial conversion is being produced by bacteria which oxidise nitrite into nitrate NO3. Having a very small NO3 reading means our biofilters (K1 chambers x 2 and Bakki showers) are very healthy. So, running our pond at a very stable pH value of 7.00 and managing the carbonates for our KH, which are around 13mg/L assisting the nitrification cycle so complements our bio filters…though as said we keep a very close eye on this when feeding heavy.


As well as our changes and upgrades mentioned above by maintaining a stable pH of 7.00 and managing a low KH we’ve noticed a difference in the koi’s skin and lustre, as said we used to use clay, we haven’t for many years now, there is no need to. All our koi now average size 7 (75cm to 85cm) and we have very little issues from parasitic areas...fingers crossed!


One of the good points with running with a pH of 7.00 is ammonia is less toxic at this low level, as our koi are always excreting ammonia. A danger point is that heavy metals such as copper, zinc and aluminium are more toxic in low alkalinity water, this is one reason why as said we have upgraded our purification system(s). On the downside with being blessed with good water our source water has a high chlorine level of 0.45mg/L, but with good purification management and regime we can eliminate this.


The answer to my question at the top of the thread: which one is more important KH or pH?  For us they both complement each other, pH for the koi, KH for the alkalinity of the pond bio converter…that is the way we look at it!


So, like everything this has been a huge learning curve for us over the years and as always still learning…Happy days!!



Koi. Organisation. International.

Syd Michell

Michael Snaden

Though to be fair there are a lot more hobbyist that now have a good understanding of the subject especially the last 6,7 years or so as we need to understand the chemistry regarding keeping water and growing our koi, more so than when we first started.

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