Carbonate hardness is the measure of carbonate and bicarbonate ions. It is commonly measured in degrees (dKH) or parts per million (ppm), and it uses the same formula discussed in last month’s column to convert dKH to ppm. (One dGH—in this case, dKH—equals 10 milligrams of calcium or magnesium oxide per liter, which is likewise equivalent to 17.848 ppm. Multiplying dGH—in this case, dKH—by 17.9 gives ppm, and inversely, dividing ppm by 17.9 gives dGH—in this case, dKH).

KH has no direct impact on fish so most fishkeepers neglect the importance of KH. But what they forget is the essence of KH. KH is normally tied to GH, since carbonate minerals include limestone, dolomite, calcium, and calcite. These minerals help buffer the pH, keeping it stable and preventing it from changing; sudden changes in pH are fatal to fish.

I was reminded recently of this fact when I read a Facebook post by a friend who was wondering why his fishes started dying one by one. He had a bare tank with a sump filter that is well maintained. He was surprised to find out that his pH had reached a dangerous level of 4.5 and the fish were slowly being killed by the water being too acidic. To rectify the situation, I recommended that he add a bag of crushed corals or oyster shells—which both contain calcium—as a chemical filter media in his sump. This will increase KH, which in turn will increase pH and keep it from becoming extremely acidic.

Since KH has a direct impact on pH—which can have an impact on the fish—it is best to remember that high KH will keep pH high and low KH will keep pH low. Therefore, to successfully keep Altum Angelfish that require low pH, your KH should also be low. Likewise, to successfully keep Blue Zaire Frontosa which requires high pH, then your KH must be high.

In closing, carbonate hardness is sometimes called “Temporary Hardness” because it can be removed from water by boiling, which precipitates out the carbonates.

Water Quality

Now let’s talk about water quality. In my own definition, water quality revolves around how clean or dirty your tank water is. Again, pure water or H2O is very clean. Again, in nature, our fish do not live in pure, ultra clean H2O. Being the universal solvent that water is, dissolved in the water mixture are organic wastes.

In the aquarium, dissolved organic wastes in the water is a big concern. Let’s face it; your aquarium, no matter how big it is, is miniscule compared to a river where the fish naturally live. Therefore, with limited volume and daily addition of organic wastes through leftover food, fish urine and feces, and other organic matter that will rot in the confines of the tank, your water will become so dirty that it will kill your fish.

The three biggest concerns when it comes to water quality in the aquarium are ammonia, nitrites, and nitrates. These are the three organic waste materials that, if left unchecked, may poison your fishes.

I would suppose every fishkeeper has heard about the nitrogen cycle since it is the basic theory in fishkeeping. But in case you haven’t, it simply means that in the aquarium set-up, organic wastes shall decompose in the water. This decomposition will undergo three processes in the filter that will transform dirty water to clean.

First, organic wastes will rot and become ammonia. With the filter providing a perfect home for beneficial bacteria to develop, nitrosomonas bacteria will inhabit the filter medium and process ammonia, converting it into nitrites. After this, nitrobacter bacteria colonizing the filter media will then process the nitrites into nitrates. This completes the nitrogen cycle, a process that converts organic waste products to highly toxic ammonia to less toxic nitrites and the least toxic nitrates.

With production of these three toxins continuing on a 24/7 basis, in some time, they will reach very high, toxic levels, thus making the water on your aquarium very dirty.

Of course our solution to keeping dirty water from killing our fishes is proper maintenance procedures. With an effective maintenance system that includes a periodic partial water change, occasional cleaning of the filters, etc., your hard work will reward you with clean and good quality water that will make your fish happy.


To successfully keep your fish, good water parameters and good water quality go together. You cannot just have one, and both should be equally of optimum standards. While your skill as a fishkeeper will definitely help you achieve optimum standards, no amount of skill or experience will be able to tell you what levels of pH, GH, KH, ammonia, nitrite, or nitrates your tank water has. Certainly there will be some signs ,but you will never be able to determine the values unless you use test kits.

Test kits for checking your water parameters and water quality are available in the market today. The Philippine fishkeeping industry has progressed by leaps and bounds over the past few years, so these test kits—which used to be rarities—now abound.

Among Filipino keepers, using test kits is, sadly, hardly practiced. But the Filipino fishkeeper is slowly understanding the benefits of doing so and the habit is picking up. If you love your fishes and care about their well- being, then invest in test kits to pinpoint the critical levels of your tank water. That way, you can take the correct actions to improve your water parameters and water quality.

Now is a good time to remember the time-tested saying, “Take care of your water and your water will take care of your fish.” Always remember that if you have optimum water parameters and optimum water quality for the kind of fish you are keeping, then you should be on your way to having healthy fish.


This appeared in Animal Scene magazine’s September 2017 issue.