pH is the measurement of wether or not the water is alkaline or acidic.a pH of 7( hydroxal iron = hydrogen irons) is neither acid or alkaline and is said to be neuatral.The more Hydrogen irons the more acidic the water and the pH number is reduced.ie very acidic 0.The more Hydroxil irons the more alkaline the water.very alkaline = 10.
KH is the carbonate hardness and is the General Hardness take away the minerals Calcium & Magnesium
KH ismeasured in deutch hardness dH seeWater Analysis
As a consequence of photosynthesis, ie during the daytime, plants remove carbon dioxide from the water causing alkaline carbonates and bicarbonates to predominate in the water and the pH. to rise. Conversely during the hours of darkness the plants will produce carbon dioxide and cause the p.H to fall.In the case of heavy algal blooms the pH of water can fluctuate quite dramatically through a 24hr period.
The relationship between K.H. p.H & CO2 can be seen in the following table/graph.
It can be seen from the above graph that for higher values of carbonate hardness (d.H) the effects of carbon dioxide in relationship to p.H are less dramatic.
For instance take a d.H value of 3 at a p.H of 7.4 and suppose the plants produced 10 mg/mltr of CO2 during the nighttime then the p.H would fall to 6.8,however if the same CO2 was produced with a higher d.H value then the p.h would only fall to 7.2.This is known as the buffering effect or reverse alkilinity.Fish excrete Ammonia which in solution gives ammonium hydroxide so pH increases. However, the nitrifying bacteria convert this ammonia into Nitrate in a reaction that releases hydrogen ions so the pH falls - in a pond or aquarium that has little or no water changes the pH may fall to unacceptable levels.
The relationship between pH and water hardness is that, generally speaking, hard water is normally Alkaline and soft water is normally Acidic. This relationship is very important when trying to alter the pH of pond water.
Water hardness is quite significant to the welfare of the Koi. Essentially, the total hardness is a measure of the ions of the alkaline earth metals, principally calcium and magnesium. Certain Koi or water treatments actually work better where the water has a high total hardness and indeed the hardness is beneficial in bonding many substances such as metal which could be detrimental to the welfare of Koi.
The Nitrification process and the addition of hard water from the tap gives ideal conditions for the growth of blanketweed, ie. fertilisers in the form of nitrates and scale-forming salts giving growth site on pond walls. Reducing these calcium and magnesium salts have a direct effect on the growth of blanketweed. Unfortunately, removing these salts,also removes the minerals which are essential to the well being of koi. It is now believed that the use of electronic blanketweed controllers change the structure of the mineral molicules( mainly calcium) thereby they cannot be utilised by blanketweed so it is not necessary to remove these essential minerals.
Due to the combined effects of large quantities of rain water,nitrification process and photosynthesis which all may reduce the p.H. to unacceptable levels. The ideal p.H suitable for Koi being between 7.5 and 8.2. It will therefore be necessary to increase the d.H of the water (buffering capacity) thereby reducing the effects of the above and preventing an unacceptable fall in the p.H. Unfortunately it is usually necessary to add those elements which also make the water harder (limestone crushed shells etc.)Thereby adding limescale to the pond and providing further growth site for the blanketweed. Fortunatly this increase in hardness will be beneficial to the fish due to the decreased workload on the fishes osmoregulatory system. As it is mainly the carbonates & bicarbonates which have the buffering capacity it is therefore better to had those elements which do not also increase the hardness to levels which would cause the prolific growth of blanket weed.One such as sodium bicarbonate(baking powder). However it is my experience after raising the K.H. by use of bicarbonate of soda(liberates CO2),this also can cause algea blooms as the blanket weed utalises the CO2 in photosythisis.It is of my opinion that the use of Merlyn(calcified seaweed) is a more natural way of buffering the water.