ALL THINGS KOI AND H2O
ARE YOUR KOI HAVING A HARD TIME?
General Hardness myths
by Mike Snaden
General Hardness myths
The purpose of this article is to offer some explanation for some of the current misconceptions about water parameters pertaining to the term General Hardness or GH. It is unfortunate that a lot of UK koi hobbyists tend to take general aquaculture knowledge, and apply it directly to Nishikigoi. In so much as what is good for intensive aquaculture rearing techniques for food
fishes are also good for Nishikigoi pond management.
The two aquatic cultures have entirely different objectives involved, in what they set out to
achieve for the end result. Japanese breeders and universities are constantly striving to perfect production, growth, and health aspects of Koi. It is accepted that the Japanese are true masters and have made important discoveries that link good koi health, excellent growth and superior
Hi development to many aspects of koi keeping, non more so than the subject of Water
Hardness. The hobby would benefit greatly from attempting to learn from the Japanese professional Nishikigoi industry.
It's all too common to hear some hobbyists say, Mains water in certain areas is too soft, and
should be hardened. It's understandable that Carbonate Hardness (KH) should be elevated,
but the same cannot be said for General Hardness. So the focus of this short article is to offer some explanation as to why this need not be the case in so many instances, and that indicators fromJapan suggest that Soft water should be nurtured and taken advantage of, not necessarily hardened! It is generally accepted in Japan by the Koi industry / breeders, that Koi growth is enhanced in soft water. Hi will become thicker, the shine of the skin (Tsuya) will improve,
and last but not least, the health of the koi will be stimulated and greatly enhanced, hence less problems. But in a general sense the koi hobby tends to believe that Koi are put into Japanese mud ponds because of the high mineral content and low stocking levels will make the Koi potentially grow larger at a faster rate than would otherwise be the case. Whilst there is an element of truth in this statement, it does not show the full picture, and can be interpreted
as a misunderstanding. The fact is many of Niigata's mud ponds have soil that is so dead from
lack of minerals, that only rice (or Koi) can be grown there. However, mud ponds do offer
benefits such as live insects, and plankton
KH Carbonate Hardness or Alkalinity.
Carbonate hardness is essential for the buffering effect it has on the pH of water in a closed
circuit koi pond. If a recorded pH of a given volume of water is 8 and an amount of acid is
added, it is commonly expected that the pH value should drop by the corresponding amount of acid added, if there were little or no Kh value to the water, this would be the case, but the
purpose of KH is to act as a buffer so rather than the acid added to the pond directly
influencing the Ph value, the acid is spent on the carbonate ions in the KH value and only
when the carbonate reserves of the kh value are used up will the acid directly influence
and lower the ph. Hence, if the KH value falls too low, causing the pond water pH to be
influenced too easily by everyday occurrences such as fish respiration, fish urine, waste by-products from filtration system bacteria, plants life and even acid rain, in short just about everything that is considered normal in a pond environment that is capable of introducing
an acid base.
So by these examples it is easy to see why KH is so important. If a pond has a low KH, and
regular pond maintenance isn't carried out, the water will lose it's buffering capability, and
the pH will fall. At first this isn't a problem, as Koi are best suited to a pH of 7.0. But, if left unattended, the pH will fall to dangerous levels, and quickly crash the system. Resulting
in acidic water, and a pond full of either very unhappy or dead Koi, as well as a dead filter. Example: A pond in an area where the water has a typically low KH value This need not be a problem if the system falls into the following criteria, I.E. the pH runs at a steady 7.0, and
pond maintenance is done religiously, perhaps at twice-weekly intervals. The pond is not overstocked; feeding is done in constant measured amounts. There is a good working
knowledge and you understand the pond system and how it functions, plus the checking of
all water parameters are done at regular intervals, leave nothing to chance. But, if non of the
afore mentioned criteria are present it would be the authors advice to keep the pond water
KH well up and therefore well buffered, or disaster will strike! A good KH level should be somewhere in the region of 2 to 6dH. There is no point in running a higher level than 6,
as this will often result in a rise of the pH.
The Japanese consider a pH of between 6.8 and 7.4 to be ideal.
GH. General Hardness.
This is a measure of the amount of dissolved solids (mineral content), E.G. calcium, iron, aluminium, manganese, magnesium, chlorides, etc. GH has nothing directly to do with the KH buffering effects of water, also a GH measurement is no indication of the KH value as the two
are totally separate independent readings. And the only thing they share in common is the
term Hardness in the title name.
For Japanese Nishikigoi professionals, the ultimate goal is to achieve low GH values.
GH can be measured as ppm or dH, (German Degrees Hardness) Many things can effect Water hardness. A typical tap water reading in the Bristol area is around 14dH (250ppm, or parts per million).
In Japan this would be considered high! However many more things can effect and raise the
GH reading of a typical koi pond. Stocking levels, feeding levels, and chemicals will raise
This is one of the primary reasons that Koi are grown-on in mud ponds. Water in a typical Japanese Mud pond, is generally between 35 and 85 ppm TDS. The stocking rates employed
with most mud ponds are kept low so that the daily feeding doesn't raise the water hardness.
It is thought by many, the main reason koi kept in Japanese mud ponds grow very quickly. Concrete Koi ponds in Japan are often overstocked, and the water is more likely to be in the region of 150 ppm TDS. This is the one of the main reasons many Japanese hobbyists put
their best Koi back into mud ponds each year, they can then grow in soft water, as opposed
to having their growth stunted with the harder water of a conventional Koi pond, Plankton and micro organisms are another reason. TDS. Total Dissolved Solids.
A TDS reading basically represents a combination of KH, GH, and any other dissolved solids.
The readings below have been taken using a Japanese TDS meter. This meter is sold in Japan
as a 'Water quality instrument'. From the TDS reading given below, we can obviously assume
that a TDS reading of lets say 80ppm, that the KH might be for arguements sake 2dH (36ppm), and hence the GH can therefore be a maximum of 2.45dH (44ppm).
This is just an example to help you understand that in a given TDS reading, a GH and KH in
total when combined, can't exceed the TDS reading, except when allowing for the innacuracy of the test.
The following are pond water statistics compiled over the past three years
Mains water pH 7.5
Pond pH 7.4,
KH- 5dH (89ppm),
GH- 13dH (232ppm)
Pond number 2 of 4400-gallon,
Rain water 30ppm (TDS).
Swansea, Mains water pH 7.1,
Pond ph 6.9,
Mains water 50ppm (TDS),
Rainwater 25ppm (TDS), After allowing the stocking density to rise, the pond now measures 154ppm TDS and it's thought that the reason for the increase in TDS is because of overstocking/overloading, and major lack of water changing. However, at 154ppm, the TDS level
of this pond is still far lower than average.
Japan, Mains water 75ppm,
Pond water (mud ponds) 35 to 108ppm (TDS)
Pond water (hobbyists ponds) 108 to 220ppm (TDS)
SWANSEA POND The pond study case in Swansea contains only 2500 gallons of water.
The pond is heavily overstocked, but the filtration system is more than capable.
And is born out by the following growth results, that were monitored very closely.
Wakabayashi male Kohaku 47cm (2000) now 61cm (March 2002)
Wakabayashi male Kohaku 39cm (March 2000), now 55cm (March 2002)
Takumi Nisai female Showa, 35cm in November 2000, now 46.5cm (March 2002)
Kumonryu (Nisai, 25cm, April 2001), now 42cm (March 2002)
Ochiba Shigure (Nisai, March 2000), now 47cm (March 2002)
Yamabuki Ogon Female (Sakai Hiroshima, Nisai in May 2001, 40cm), now 55cm (March 2002) Dainichi Tosai Kohaku (April 2001, 23cm) This Kohaku was exhibited at the BKKS National
2001, survived, and now measures 39cm (March 2002)
Wakabayashi female Sanke 37cm (2000), now 48cm (March 2002)
Sakai (Hiroshima Showa), Tosai in June 2000 at 27cm, now 53cm (March 2002)
Dainichi Showas X5. These Koi were between 20 and 25cm in when put into Colin's pond in October 2001 (Tosai of May 2001), and now, one measures 33cm, three measure 40cm, and one measures 42cm (March 2002). Tancho Kohaku (Nisai), of 18cm in September 2000, now 43cm (March 2002).
All of the above Koi were supplied by us, and in addition to these Koi, there also reside several other Koi of various origins. One of them is a Chagoi which I remember two years ago as being about 45cm, which now measures some 68cm! So, as you can see, the stocking level of this
pond is pretty much outrageous!
A further point of interest is that the filter system used is a "RTF 3500", which I have heard
some people criticise. Although the design of this filter system is a little unorthodox, it works
very well indeed. Colin is now about to dismantle the pond, in order to build a bigger one of
about 7000 gallons. The original filter will be retained, but fed from one drain. A second drain
will feed into an additional set of RTF filters.
Many other Koi supplied have achieved similar growth rates. Also, other Koi supplied and placed into similar water in the West Wales and the Welsh Gower area, have achieved similar growth. BRISTOL POND
The Bristol pond case study is some 7800 imperial gallons. Despite being run at similar temperatures, and similar feeding rates to the Swansea case study, the Bristol pond cannot achieve the same growth rates. The only Major difference that is apparent, between the two
ponds, is water hardness. The best growth rate to date from the Bristol case study was a Koi growing from 37cm (April 2000) to 45cm (December 2000). Also, a Shiro Utsuri, growing from
34 cm (September 2000) to 45cm (May 2001).
These two koi were the only exceptions to the rule. And the normal growth rates for the Bristol case study, other ponds in the area have achieved similar growth but, generally typical growth rates for the higher TDS readings in the Bristol area would be disappointing when compared to what can be achieved in the areas where softer water is prevalent.
But there is no doubt that ponds in Bristol area with a lower GH have growth rates better than those with a higher GH.
Typical Japanese case studies are as follows; these figures are for various major Japanese
breeders mud ponds in the Hiroshima area. All of the readings are TDS readings, and hence represent a total of GH and KH levels combined. A 'PPM' figure should be devided by 17.9 to obtain a dH reading.
Wakabayashi 65 to 78ppm,
Takumi 76 to 85ppm, Takigawa 105 to 108ppm,
Imai 35 to 48ppm,
Inoue 35 to 48ppm,
Momotaro 75 to 85ppm.
Naturally, all of these ponds have growth rates equal to but mainly greater than the pond in Swansea! But, temperature in Japan also plays a large part. Other points to remember Feeding raises GH, Fish waste raises GH, Iron, salt, and calcium raise GH, High Nitrates raise GH.
Zeolite lowers hardness a little, as do Ion exchange resins.
If you really feel that you must raise GH / TDS levels, then overfeeding is the fastest way to do
it! (not advised).
MOMOTARO KOI FARM Momotaro is certainly one of the top 5 breeders in Japan.
President Maeda (Mr Momotaro) feels anxious when growing Koi in mud ponds.
President Maeda, feels that once Koi are placed into mud ponds; things are no longer in his control. Consequently, President Maeda is much happier growing Koi in concrete ponds,
as the Koi can be carefully watched, and their growth and development can be carefully
controlled.This is an area where Momotaro Koi Farm excels!
President Maeda has developed a new filtration media. This media has an appearance of coral,
but is a man made material, which is baked at high temperature. This media is used in his
filter systems, and also in multi level trickle filters. These trickle filters obviously remove
Nitrates, but also lower hardness!
President Maeda say's that low water hardness and low Nitrates are of the utmost importance
in the quest for maximum growth and good development in Koi. Using such methods,
President Maeda has achieved the following Around 1997,
Momotaro managed to produce a Tosai Kohaku of 51cm! Despite such fast growth, the Koi maintained wonderful quality.
He has also grown the first ONE METRE GO-SANKE!!! But, unfortunately, the famous
1,000,000-yen prize did not exist! It was the monetary value placed upon the prestige
of being the first person to grow a one-meter go-sanke.
After asking several breeders in Japan about the topic of water hardness, it was said by all,
that soft water is essential in order to grow large Koi, further, good Hi quality, Teri (lustre)
and Tsuya (shine) is also considered to develop well in soft water.
But, the opposite is true for good white ground, requiring slightly harder water conditions.
Mr Izeki of Izeki Products is quoted as saying that, he considers a water GH value should
be as low as possible, also if GH measures 3 dH (51ppm) or over, it should be lowered.
Mr Izeki achieves excellent, growths rates equal to mud pond growth rates in his concrete
ponds by maintaining low GH values.
In the September of 1999 issue of "Nichirin", the ZNA Japanese Koi magazine there is an
article entitled "Basic Koi Keeping" subtitle, Water Hardness. This article was supervised by,
Dr Takeo Kuroki (Honorary Chairman of the ZNA), Mr Nobuo Takigawa (Chief of the Keeping
Skills Bureau), and Professor Ken Sasaki (of Hiroshima Kokusai Gakuin University).
(quote): "Hardness. Hardness is an indication of the amount of calcium or magnesium;
the lower this is the better suited the water is to the raising of Nishikigoi. A reading below
50ppm (2.92dh) is considered desirable. This degree of hardness is also said to control the appearance of the Hi and the Sumi".
WATER HARNESS SHOCK When Koi are harvested and put into hard water, they can
sometimes roll onto their sides. The Japanese professional refer to this as Water Hardness
Shock. A transition from soft to hard water is believed to causes Koi great discomfort and
stress; hence they may sit on the bottom and are often to be seen rolling over on their sides. It usually takes about three days for the Koi to adjust to the water hardness and behave normally. This can also happen when Koi are sent from Japan to England, despite sometimes the water being hardened in Japan prior to shipping, this effect can still be observed from time to time, however, the Koi soon adjust. It is also accepted in Japan that Koi are more resistant to disease and also heal at a faster rate in softer water. Note: Water hardness shock does not occur in the case of a Koi being moved from hard into soft water.
There are two routes to take with hardness levels in your pond.
HIGH GH LEVELS
Good white ground and sumi development, but poor growth rates. (Ideal for those that are
hoping to show their Koi, or those that have less time to devote to pond maintenance).
LOW GH LEVELS. High growth rates, deep and even Hi,
but weaker white skin, and slower Sumi development. Bear in mind however, that just a few
weeks in hard water will improve the white skin ready for a Koi Show. It would be preferable to definitely go for the latter approach, it could be viewed as a waste of time and money to invest
in buying an expensive Koi, and then restrict it's growth an development. From a personal
point, I have just purchased a water softener. This unit uses ion exchange resins to remove
the GH ions, and substitute them for Sodium ions. In practice, this unit will completely 'zero'
the GH, so it is essential to allow some water to bypass the unit in order to obtain the desired
Copyright © FEBRUARY, 2002, M Snaden, ALL RIGHTS RESERVED