Saturday, April 4, 2009

Water quality … pH, GH, KH Oh my!

I want to touch up a little on the water quality. And what I learned after reading and reading on this subject. If there is some mistakes I hope that someone can correct me.
Water is more that just simple combination of hydrogen and oxygen. Water can be describe as hard or soft, and alkaline or acidic, and it acts as a carrier for a wealth of nutrients, toxins, bacteria (both beneficial and harmful), as well as pollutants. Providing good water quality means ensuring that all these factors are at the correct levels so that the water in the aquarium is not only safe for plants and fish but also actively encourages their health and growth. In nature water is rarely pure in the “distilled water” sense; it contains dissolved salts, buffers, nutrients, etc. with exact concentrations dependant on local conditions. Plants and fish have evolved over million of years to the specific water conditions in their natural habitat and may be unable to survive in significantly different environment. As a beginner I think it’s a good idea to select plants and fish whose needs match the qualities of your tap water. An advanced aquarist can change water characteristics there is many ways to do it but its way more complicated than first appears and could potentially cause more problems. In any case I think it’s important to be familiar with water chemistry to ensure that plant and fish in your tank are healthy and happy and have the best suitable environment.
Water has 4 measurable properties that are commonly used to characterize water chemistry. They are PH, buffering capacity (KH, Alkalinity) general hardness (GH) and salinity. In addition there are several nutrients and trace elements, but I won’t be discussing those. The only things I will talk about are pH, GH and KH.


pH refers to water being an acid, base, neutral or alkaline. A pH of the water is a measure of the balance between the hydrogen (H+) and hydroxide (OH) ions in the water. I think most know that low pH means that water is acidic, high pH is alkaline (or basic). So pH of 5 is slightly acidic water, pH 7 is neutral and pH of 8 is alkaline water. There is one very important point and if you mathematician you will see it. The pH scale is a logarithmic scale. In other words a pH of 6.0 is 10 times more acidic than pH of 7.0 and a pH of 5.0 is 100 more acidic than pH of 7.0. When keeping fish is very important to understand that slight and sudden change in pH is very stressful to fish than it might first appear. Remember that it’s not a difference of 1 when you go from 6.0 to 7.0 it is 10 times more, if the difference is 2 it’s 100 times more, 3 a 1000 times more and so on.
In fish keeping hobby pH is very important because rapid changes in pH are very stressful to fish and should be avoided. Changing ph by more than .3 units per day is known to stress fish. And that’s why you want to have the pH in your tank to remain constant and stable. Fish have adapted to thrive in a certain pH range in their natural habitats so you want to make sure that your tanks pH matches the specific requirements of the fish you are keeping.
Most fish can adjust to a pH somewhat outside their optimal range. If your water’s pH is naturally 6.5-7.5 you will be able to keep most fish species without problems and there is no need to adjusts your pH.

Ways to lower pH
Filtering water over peat
Add bogwood to the tank
Injects carbon dioxide CO2
Use a commercial acid buffer
Water changes with soft water or RO (reverse osmosis) water

Ways to raise pH
Aerate the water, driving off the carbon dioxide (CO2)
Filter over coral or limestone
Add rocks containing limestone to the tank or use coral sand substrate
Use commercial alkaline buffers

Here is a pH scale

Carbonate Hardness (KH, alkalinity) or Buffering capasity

This is were lot’s of people get confused and me too, so I hope writing about it will make it a little less confusing for me and hopefully will be helpful to anyone who reads my blog. Sometimes the term alkaline is avoided and the term basic is used for the pH scale is because this reading is measuring the alkalinity of the water. IT IS NOT THE SAME AS ALKILINE. In fresh water aquariums most of the water’s buffering capacity is due to carbonates and bicarbonates. That’s why the terms “carbonate hardness” (KH), alkalinity and Buffering capacity are used interchangeably. They are technically not the same things; they are equivalent in practice in the context of fish keeping. Again I will remind that “alkalinity” should not be confused with the term “alkaline”. Alkalinity refers to buffering, while alkaline refers to a solution that is base i.e. pH higher than 7.0. So alkalinity is a measurement of waters buffering ability, the ability to absorb and neutralize acid. The pH and buffering capacity are intertwined with one another. If the water has a sufficient buffering capacity, the buffering capacity can absorb and neutralize added acid without significantly changing the pH, so the more alkalinity or carbonate hardness in the water the less likely swings in pH. A buffer acts like a sponge, as more acid added the “sponge” absorbs the acid without changing pH. But the buffering capacity is limited, once the capacity is used up the pH changes more rapidly as acids are added. The nitrogen cycle produces nitric acid (nitrate). Without the buffering the tanks pH will drop over time (a bad thing). With sufficient buffering capacity the tanks pH stays stable (a good thing). Hard tap water almost always has a large buffering capacity. If the pH of the water is too high for your fish the buffering capacity makes it difficult to lower the pH to more appropriate value. That’s why when people try to lower pH without fully understanding the water chemistry usually fail because buffering effects are ignored. How much buffering does the tank need? There is aquarium buffering capacity test kits available that actually measure KH. The larger KH, the most resistant to pH changes the water in the tank will be. Tank’s KH should be high enough to prevent large pH swings in the tank over time. If KH is below roughly 4.5 dH, the regular test of the waters pH are required, roughly once a week to get a feel how stable the pH is. It’s especially important if regular partial water changes are not performed. The nitrogen cycle in the tank creates a tendency for an established tank’s pH to decrease over time. If pH drops more than 2 tenths of a point over a month, increasing KH should be considered, or performing partial water changes more frequently, which I think is easier to do as a routine. It is never a good idea to add or use distilled or any pure water for the tank. That means that adding even a little bit of acid will change pH significantly and will stress fish. The good thing is that KH does not affect fish directly.
Ways to increase KH
Adding sodium bicarbonate (baking soda), one teaspoon of baking soda to 50 litters (around 13.2 gallons) of water can raise KH of water by approximately 4 deg dH without major affect on pH.
Adding an air stone to increase surface turbulence driving off CO2
Adding commercially available products to increase buffering capacity

Ways to lower KH
Increasing co2
Use reverse osmosis (RO) water. Mixing RO water with tap water until desired KH is achieved
Adding commercially available products to decrease the buffering capacity
General hardness (GH)

General hardness or GH is a measurement of magnesium and calcium ions in the water. This is measured in the German degrees of hardness scale or parts per million. When fish are said to prefer soft or hard water it is GH and not KH that is being referred too. So the pH, KH and GH form a Bermuda triangle of water chemistry, they are all distinct and they all interact with each other to certain degrees, making it difficult to change one with out impacting the other. That is why it’s better not to tamper with water parameters unless absolutely necessary. Here is an example; hard water usually comes from limestone aquifers. Limestone contains calcium carbonate which when dissolved in water increases both GH (from calcium) and KH (from carbonate) components. Increasing KH usually increases pH as well. Theoretically the KH acts as a sponge absorbing acid present in the water, raising the water’s pH.

Water hardness follows the following guidelines. The unit dH means “degree hardness”, ppm means parts per million which is equivalent to mg/l in water. 1 unit dH equals 17.8 ppm CaCO3 (calcium carbonate). Most test kits give the hardness in units of CaCO3 it means that the hardness is equivalent to that much CaCO3 in water and does not mean it actually came from CaCO3.
Here is a table that shows comparison between ppm, the dH scale and the generalized concept of soft and hard water.
General Hardness Table
0 to 4dH 0 to 70ppm---> Very soft
4 to 8dH 70 to 140ppm---> Soft
8 to 12dH 140 to 210ppm---> Medium hard
12 to 18dH 210 to 320ppm---> Fairly Hard
18 to 30dH 320 to 530ppm---> Hard


  1. Very informative posts !

  2. great post... Ive been struggling with my platties and PH... my water changes were from the house tap that is very soft so the acid from the nitrogen cycles were killing them... the other fish were ok but Im sure stressed too... I added an air stone and a teaspoon of baking soda to the 10gal tank and it is a life saver... I am now making my water changes from the non-soften facuet in my home and all is well .. the soft water is great for showers and dishes but tough on fish... thank you!