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Lake Malawi (also known as Lake Nyasa) is one of the African Great Lakes and is home to an extraordinary diversity of cichlid fishes. To successfully keep Malawi cichlids in aquariums, it is essential to understand the physical and chemical properties of the lake’s water. Unfortunately, a lot of information available online about Malawi water is incomplete or even incorrect, which often leads to confusion among aquarists.

One of the most important characteristics of African Great Lakes water—Malawi included—is that carbonate hardness (KH) is higher than total hardness (GH). This is very different from most tap water, where KH typically represents around 80% of GH (for example, if total hardness is 15°dGH, carbonate hardness is usually around 12°dKH).

The goal of every good aquarist is to provide fish with conditions that resemble their natural environment as closely as possible. Besides aquarium size and layout, water quality is undoubtedly one of the most important factors. Of course, it is impossible to fully replicate nature, as an aquarium is a closed system (the same applies to the water). Fish can adapt to a certain degree of deviation, but these deviations should not be excessive.

For wild-caught fish (imported directly from the lake), it is recommended to adjust water parameters as close as possible to natural values, although this is not always easy. For captive-bred fish, some deviation is acceptable, as many of these fish have been bred in aquariums for generations and are partially adapted to such conditions. The table below shows natural Lake Malawi parameters and recommended or acceptable values for aquariums. If you are inexperienced and your tap water does not deviate significantly from the recommended range, it is often best not to “fine-tune” parameters excessively—stable conditions are more important than chasing theoretical perfection.

Core Water Parameters

Malawi	Lake values	Aquarium values
Temperature	23–28 °C	25–26 °C
pH	7.8–8.5	7.6–8.7
Total hardness (GH)	3–5 °dGH	3–15 °dGH
Alkalinity (“aquarium” KH)	6–8 °dKH	6–12 °dKH
Conductivity	210–285 µS/cm	up to 500 µS/cm

Temperature

The best approach is to keep Malawi (and Victoria) cichlids at temperatures similar to those found in their natural habitat. In Lakes Malawi and Victoria, surface water temperature varies by about 5 °C depending on the season, while deeper layers remain largely stable. In aquariums, it is best to aim for mid-range values (see table above).

Malawi cichlids do not tolerate high temperatures well. At higher temperatures fish become more active (and often more aggressive), metabolism increases (and so does food demand), and breeding activity may increase. However, the most dangerous consequence is oxygen deficiency. At higher temperatures, oxygen dissolves less efficiently in water, which can be observed as rapid gill movement and gasping at the surface.

Temperatures around 30 °C may be tolerated for short periods, but prolonged exposure—especially above 30 °C— can quickly become fatal. At recommended temperatures (around 25 °C), fish remain active but less aggressive and will still breed successfully. At excessively low temperatures, fish may enter a form of dormancy, which is also undesirable. Therefore, stick to the recommended temperature range.

pH

pH indicates whether water is acidic or alkaline. It is measured on a scale from 0 to 14, where 7.0 represents neutral water, values below 7.0 acidic water, and values above 7.0 alkaline water. African cichlids require alkaline conditions (above pH 7.0).

pH is influenced primarily by carbonate hardness (KH) and the concentration of carbon dioxide (CO₂). Because CO₂ levels fluctuate due to biological processes in the aquarium, pH can also change. Higher KH provides greater buffering capacity and therefore a more stable pH.

pH can be regulated in various ways. It can be lowered by adding reverse osmosis (RO) water, which reduces KH (and GH) and consequently lowers pH. This method is almost never necessary for African cichlids, as tap water usually already has suitable carbonate hardness.

If pH is too low, it can be increased by adding buffers that raise KH. This may be relevant only if your water is very soft with low KH (which is uncommon in many regions). For Malawi and Victoria cichlids, products such as Seachem Malawi/Victoria Buffer can be used. These increase KH without affecting GH.

Although many options exist for pH adjustment, it is strongly recommended not to experiment with pH regulation unless values are clearly outside acceptable limits—especially if you lack experience. It is very easy to unintentionally affect other parameters or cause pH instability. A stable pH that is slightly off target is far safer than one that constantly fluctuates.

Water Hardness

Water hardness is extremely important for fish health. It affects osmoregulation and calcium balance in the blood, and it also influences the toxicity of certain substances. In general, harder water reduces the toxicity of many compounds; however, there are exceptions—ammonia, for example, is far more toxic in hard, alkaline water due to higher pH levels.

Contrary to what is often stated online, Lake Malawi water is not hard—it is actually soft, with GH values of about 3–5 °dGH (similar to Lake Victoria). Malawi cichlids are, however, highly adaptable and can adjust well to harder water, especially captive-bred fish. Based on decades of aquarist experience, keeping Malawi cichlids in slightly harder water does not appear to cause major negative effects.

We distinguish between total hardness (GH) and carbonate hardness (KH). A notable feature of African Great Lakes is that KH is higher than GH.

Total hardness (GH)

Total hardness measures the concentration of alkaline earth metal ions in water, regardless of their chemical form. These metals include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). In practice, GH is determined mainly by calcium (Ca²⁺) and magnesium (Mg²⁺), while the other elements occur only in trace amounts.

GH can be increased by adding calcium or magnesium salts (for example magnesium sulfate / Epsom salt, MgSO₄, or calcium chloride, CaCl₂) without affecting carbonate hardness (KH). If calcium or magnesium carbonates/bicarbonates are added (such as calcium carbonate / limestone, CaCO₃, or magnesium carbonate, MgCO₃), both GH and KH will increase.

GH is expressed in degrees of German hardness (°dGH). Sometimes hardness is given in ppm, where 1°dGH = 17.8 ppm. Water hardness is commonly categorized as follows:

0–4 °dGH	0–70 ppm	very soft water
4–8 °dGH	70–140 ppm	soft water
8–12 °dGH	140–210 ppm	moderately hard water
12–18 °dGH	210–320 ppm	hard water
18–30 °dGH	320–530 ppm	very hard water

Carbonate hardness (KH)

Carbonate hardness (KH) represents the portion of total hardness related to alkaline earth metals (mainly calcium and magnesium) bound to carbonates and bicarbonates. In many waters, KH is roughly 80% of GH and can never exceed GH in the strict chemical sense.

So how can KH be higher than GH in Lake Malawi? The reason lies in how aquarium KH tests work. Aquarium KH tests do not measure true carbonate hardness—they measure alkalinity, which is the water’s ability to neutralize acids (buffer capacity). Alkalinity includes all bicarbonates in water, not only those associated with calcium and magnesium.

For example, if sodium bicarbonate (baking soda, NaHCO₃) is added to RO water (GH = 0, KH = 0), true GH and true KH remain zero, but aquarium KH tests will show an increase because they detect bicarbonates regardless of the associated cation.

From an aquarium perspective, alkalinity (“aquarium KH”) is important because higher buffering capacity results in more stable pH. This stability is critical, as fish are sensitive to large and especially rapid pH fluctuations.

Na, Ca, Mg and K in Lake Malawi

Chemical element	Malawi
Na (sodium) mg/L	21.0
Ca (calcium) mg/L	16.4–20.7
Mg (magnesium) mg/L	4.7–8.8
K (potassium) mg/L	6.4

Conductivity

Conductivity measures the ability of water to conduct electrical current. It depends on the concentration of dissolved ions and water temperature. For comparison: seawater has a conductivity of about 50,000 µS/cm, rainwater about 5–30 µS/cm, and RO water close to 0 µS/cm.

Conductivity is often confused with water hardness, but they are not the same. Two waters with the same hardness can have very different conductivity values, because conductivity is also influenced by ions such as sodium and sulfate, which do not contribute to hardness.

Nitrogen Compounds

Ammonia (NH₃/NH₄), nitrite (NO₂), and nitrate (NO₃) are products of biological filtration (the nitrogen cycle). Whether ammonia or ammonium dominates depends on pH: at pH below 7.0 ammonium (NH₄) is favored, while at pH above 7.0 ammonia (NH₃), which is far more toxic, becomes dominant.

Because Malawi aquariums are alkaline, efficient biological filtration is essential. Ammonia and nitrite must always be 0 mg/L. Nitrate should ideally remain below 25 mg/L and as low as possible. In Malawi aquariums, regular water changes are the primary method for controlling nitrate.

Oxygen

Oxygen is essential for fish and for the bacteria involved in biological filtration. Water contains about 30 times less oxygen than air. Oxygen solubility decreases with rising temperature, making aeration especially important during warm periods.

Adequate surface agitation (filters, circulation pumps) and/or air pumps are necessary to ensure sufficient oxygen levels. Lake Malawi is well oxygenated in its upper layers, so strong oxygenation in the aquarium closely matches natural conditions.

Water Changes

How often?

There is little debate here: experienced aquarists recommend changing about 50% of the water weekly (or at least every 10 days) in Malawi and Victoria cichlid aquariums. Without regular water changes, fish health will inevitably suffer.

Why?

Nitrate accumulation is one reason, but not the only one. Lake Malawi is an exceptionally clean lake, with very low microbial counts. Even “clean” tap water often contains more microbes than lake water, and feeding plus fish waste rapidly increase microbial load in aquariums.

Regular water changes remove dissolved waste and help maintain conditions closer to those found in the natural environment. More frequent changes are beneficial and safe—even daily for fry— as long as temperature and water parameters remain consistent.

Should you age water (24 h) or not?

This topic has been widely discussed (not only because of chlorine). My recommendation is to age water for 24 hours whenever possible and to use a water conditioner (for example, Seachem Prime).