Practical Water Chemistry

Practical Water Chemistry
by Shelie Wittig ( Fishgal )

Water chemistry can be a bit daunting to the beginner aquarist; at least it was for me. When I got started in the hobby I was sold a complete “test laboratory” which included tests for 5 different things. I was diligent about testing and recording the results, but never had a very good understanding about what these properties were and how they affected my fish. This made it very difficult to actually use any of the data I was collecting.

As it turns out, it’s not really all that complicated. Fish keepers are mainly concerned with how acidic or alkaline the water is, and what concentration and variety of dissolved minerals it contains. These are expressed by measuring three basic properties: pH, GH and KH.


pH is probably the single most important property to understand and monitor. It refers to water being acidic, basic (alkaline) or neutral. With a measurement of 7 being neutral, less than 7 is acidic and greater than 7 is alkaline. While common tropical fish are happiest right around neutral, African cichlids prefer the following alkaline ranges:

Lake Malawi species:    7.4 – 8.6
Lake Tanganyika species:    7.8 – 9.0
Lake Victoria species:    7.2 – 8.6

Fish are extremely sensitive to changes in pH and it is important to maintain a stable level in your aquarium. When adjustment is necessary, avoid changes greater than .3 units per day – keeping in mind that the pH scale is logarithmic (like the Richter scale used to measure the intensity of earthquakes). This means, for example, that a pH of 8.0 is 10 times more alkaline than a pH of 7.0.

GH (General Hardness)

General hardness or “total hardness” is a measure of the magnesium and calcium in the water. Africans are most likely to appear vibrant and colorful in aquariums with a general hardness ranging from 160 – 320 ppm (parts per million) or 9° – 18° DH (“Deutsch hardness”). Because DH values refer to a German hardness scale, I have heard GH mistakenly referred to as “German hardness” which is incorrect. This is a mix-up between the particular water property being measured and the scale on which the result is expressed. There is also a “Clark scale,” but since I am not personally familiar with it and don’t know how widely it is used I chose not to calculate the target range using that scale. Examine your test kit carefully so that you are certain what scale it uses. The following conversion table may be helpful:

1° DH = .65° Clark = 17.9 ppm
It should be noted that GH levels naturally drop over time because minerals do not stay suspended in water very long. This is one of many good reasons for regular partial water changes.

KH (Carbonate Hardness)

Carbonate hardness, also known as “buffering capacity” or “total alkalinity,” is a measurement of carbonates and bicarbonates in the water. It is best described as water’s ability to keep the pH stable as acids or bases are added – almost acting like a sponge for those additives so they cannot affect the pH. Without adequate buffering, the pH in your aquarium will eventually drop because the end result of the nitrogen cycle is nitrate (nitric acid), which slowly builds up between water changes. With sufficient buffering the pH remains stable. For a Rift Lake aquarium, KH is ideally in the range of 180 – 240 ppm, or 10° – 14° DH.

Do I really want to tamper with these properties?

Some people are diligent about testing and taking calculated steps to achieve specific targets, while others defiantly reject that approach and claim to have a thriving aquarium without complication or added expense. I believe that success with the latter would not be without a fair degree of luck. Some hobbyists are fortunate to have hard water with a high pH right out of the tap and still others have selected species that are more adaptable than others to unnatural conditions.

With a little experimentation and application of the basic knowledge derived here, you can take a more proactive approach and perhaps even find that the challenge of creating the perfect water chemistry makes aquarium maintenance more fun. You will be rewarded with healthy, colorful fish that flash their fins, exhibit natural behavior and even spawn. More importantly, you’re much less likely to have to deal with unexplained illness or death.

How do I make changes?

To raise KH and pH, add baking soda (sodium bicarbonate). A baseline recommendation is 1 teaspoon per 5 gallons of water (dissolve in a cup of aquarium water if adding directly to the tank). For an established aquarium, remember to take this slowly as fish are highly sensitive to pH changes. Incidentally, there are off-the-shelf products available for this purpose, but baking soda is cheaper and most people already have it on hand. Wardley’s product Raise pH® is sodium bicarbonate, whereas Aquarium Pharmaceuticals’ pH Up® is sodium hydroxide.

Instead of relying solely on additives for buffering, you can use crushed coral, crushed oyster shell, crushed limestone, aragonite or dolomite as a substrate. Seashells, limestone rock or Texas Holey Rock (also limestone) will all help to provide continuous buffering as they leach carbonates into the water.

Driftwood (use only safe and sterile pieces intended for introduction into an aquarium) will leach tannic acid and consequently lower pH. It can discolor the water as well, and is typically not recommended for Rift Lake aquariums. Sodium Biphosphate (offered by Wardley) reduces pH, and pH Down® by Aquarium Pharmaceuticals contains sulfuric acid to accomplish the task. I consider intentionally lowering pH a tricky and dangerous business because it is impossible to do without affecting KH. You must first “use up” the buffering capacity and then any further steps you take will immediately lower the pH. The danger is that with no buffering capacity remaining, your resulting lower pH is extremely susceptible to fluctuation. Luckily, African cichlids like a high pH and most of us need never take any steps to lower it.

To raise GH, add Epsom salt (magnesium sulfate). A baseline recommendation is 1 tablespoon per 5 gallons of water (dissolve in a cup of aquarium water if adding directly to the tank). While adjusting total hardness is not as potentially dangerous to your fish as adjusting pH, dramatic changes of any sort can be stressful. “Flashing” (rubbing on the gravel or rocks) is often attributed to changes in hardness. Personally, I would make any substantial GH adjustment over a period of 2 to 3 days if my aquarium were already stocked with fish.

Rockwork in your aquarium helps with hardness too. While the effects are negligible (except with limestone, which is mostly calcium carbonate and therefore works on GH and KH), total hardness is likely to be higher with rocks in the tank than it would be without. Limestone, Texas Holey Rock (also limestone), pagoda, tufa, lace, petrified wood, quartz, slate, marble, and even common river rock can all be used in your aquarium safely. Be sure to thoroughly clean and sterilize (boil) anything suspect before putting it in your tank.

Hard water can be softened by diluting it with distilled water, but it is rarely necessary to lower GH for an African cichlid aquarium. While researching for this article I spoke with an individual whose water comes from a well and is extremely hard. He dilutes it with both R/O water (reverse osmosis) and water run through a home water softener, just to bring the total hardness down to 40° DH. Apparently his cichlids (both Malawians and Tanganyikans) are unable to read the test strips because they are doing just fine in both of his aquariums!

Where do I start?

The best place to start is with your tap water. Test it, experiment with Epsom salt and baking soda, retest, and determine what ratios are needed to properly condition the water you will add during scheduled water changes. Test your tank water between changes to be sure your measures are sufficient.

NOTE: To test your tap water for pH, de-chlorinate a sample and then circulate/aerate it for at least 60 minutes before testing (overnight would be even better). This will allow any gases to escape that could temporarily lower pH and skew your test results.

Is there anything else I need to add?

Aside from products to treat your tap water for toxins (see “Water Treatment”) you can provide a fine environment for your African cichlids simply by using Epsom salt and baking soda to obtain pH, GH and KH in the ranges suggested here. Still, some people like to take it a step further and use additives to provide other trace elements found in the Rift Lakes. They believe that creating conditions as natural as possible will result in extraordinarily healthy and colorful fish. Other folks feel that since most of these fish are bred and raised in aquariums, they would not miss the precise chemistry of lake water they’ve never even been exposed to.

Since beginners are likely to be overwhelmed with the various opinions and products available, here are a few basic options for working with your water chemistry, listed from most economical to least.

    • Create your own “Rift Lake Buffer/Cichlid Salt” with Epsom salt, baking soda, and salt. You can use aquarium salt or table salt (baseline recommendation is 1 teaspoon per 5 gallons of water). They are the same thing – sodium chloride (NaCl) – except that table salt often contains iodine and anti-caking agents. There are some people that warn against the additives in table salt, but just as many people claim to use it successfully. If it concerns you, buy aquarium salt. Sodium and chloride are both found in the Rift Lakes, and salt contributes to the fishes’ protective slime coating.
    • Use Epsom salt and baking soda to get the three critical properties within range, and a Rift Lake product (such asKent Rift Lake Trace Elements®) OR a marine salt (such as Instant Ocean®) to provide additional trace elements. Some people prefer to stick with products specially formulated for the Rift Lakes, while others have had great success with marine salt. Incidentally, I’ve heard that marine salt is particularly beneficial in planted aquariums.
  • Go with off-the-shelf products for everything. There are quality products offered by Kent and SeaChem (for example) that deal with the basic chemistry, buffering and trace elements. When combined into one product, it is sometimes referred to as “cichlid salt.” With the information contained herein, you should be able to read the labels on these products and have a better understanding of what they are supposed to do. Test your water to be sure they are living up to their claims.

Other Conditions to Monitor

Be sure that you have a good understanding of the nitrogen cycle. A properly cycled aquarium should test zero for ammonia andnitrites, but nitrates slowly build up in your aquarium and should be monitored. Nitrates are kept in check with regular partial water changes, and are not really so much of a “water chemistry” issue as a “water quality” one.

Provide sufficient surface agitation to oxygenate your tank water and allow CO2 to escape.

Maintain a constant temperature in your aquarium. The acceptable range is 74 – 81°F, and many experienced hobbyists recommend something in the mid range, around 76 – 78°F. High temperatures speed up metabolism and can result in more aggression. Invest in a quality heater to avoid disasters such as overheating or failure. A good thermometer is important too – do not rely solely on the thermometer on the heater. I look at my thermometer often to be sure the heater is working correctly. By doing so, I once averted potential disaster when an inexpensive heater failed to shut off after the set temperature had been reached. Lastly, be sure to match the tank water temperature when making water changes to avoid stressing your fish. □