The Science of Nature Aquariums

Understanding what’s going on in your tank will help you provide the optimal environment for your fish and plants.


The Nitrification Cycle

When organics starts to build up in the form of fish waste, uneaten food or decaying plant life, toxic ammonia levels becomes harmful to fish.

Thanks to mother nature, two kinds of bacteria convert the toxic ammonia to harmless nitrate (NO3), a chemical that fish can tolerate at moderate levels in an aquarium. These bacteria grow inside the filter system and require an abundant supply of oxygen to convert ammonia to NO3. A typical new tank will take around three to four weeks for the ammonia level to go down to zero. Only when ammonia levels are at zero is it safe to introduce fish into the Nature Aquarium.


Essential Water Chemistry for Plants

pH measures whether water is acidic or alkaline. For example, lemon juice is acidic and deep well water is alkaline. A pH of 7 is neutral, pH below 7 is acidic and above 7 is alkaline.

Plants benefit from slightly acidic water conditions. The best pH value for aquatic plants is around 6.4.

gH measures the general hardness of water. When you take a shower in hard water (like deep well water or brackish water near the sea), it is difficult for soap or shampoo to produce bubbles; on the other hand, in soft water soap feels slippery on your skin and difficult to remove. gH includes all dissolved solids, but we are most interested in the total calcium and magnesium in the water. Calcium and magnesium are important to plant growth. In most cases, a gH value of 4 is best.

gH also includes carbonate hardness (kH), which measures the amount of carbonate ions and is directly related to the ability to maintain stable pH in the water. The more kH ions available, the less pH fluctuates in the Nature Aquarium. The presence of kH also makes it easy for plants to absorb CO2, which is usually introduced in the form of calcium carbonate. However, it’s possible to have a very gH and a very low kH when the water does not contain any carbonates, but other forms of dissolved solids. The best value kH is 4 for aquatic plants.

Scientists have discovered that values of pH and kH determine total CO2 concentration. A pH value of 6.4 and kH value of 4 provide the highest concentration of CO2 (33ppm). CO2 concentration starts to climb as the kH value increases, and peaks at a value of 4. As kH goes beyond the value of 4, the CO2 concentration starts to decrease again.

As much as possible, we want calcium and magnesium to be the only solids that will contribute to water hardness, as they are what promote to plant growth. To achieve this, we usually use a reverse osmosis system to remove all dissolved solids first and then add back the carbonates in the form of calcium carbonate, and magnesium in the form of magnesium sulfate (Epsom salts). This way, we have total control of the kH and gH in the Nature Aquarium and we know that the only dissolved solids are in the form of calcium and magnesium.

Nitrate is a plant nutrient and a byproduct of the nitrification cycle (the process in which beneficial bacteria converts organic waste into nitrates). Too much nitrate will cause an imbalance of nutrients in the system, which can trigger an algae bloom. (If this happens, it can easily be resolved by techniques in algae prevention and removal.) Nitrate should be at a maximum of 30ppm to avoid algae problems. However, many need to dose nitrate daily because the plants absorb it all during the photoperiod.

Phosphate is a plant nutrient that comes mostly from fish food. Phosphate is required for root development and plant growth; however, excessive phosphates will also result in an unwanted algae bloom. Phosphate should have a maximum value of 2ppm.

Iron is an important plant nutrient that keeps plant leaves a deep green, and it also enhances the tone of red-leaved plants.

How Do We Measure Water Chemistry?

ADA offers a whole range of test kits called the ADA Pack Checker that will give you accurate readings of your aquarium’s water chemistry. These tests are used by comparing the colours inside the test vials against a supplied colour chart. ADA offers Pack Checkers for pH, TH (total hardness that includes gH and kH), NO2 (nitrite), NH4 (ammonium), NO3 (nitrate), PO4 (phosphate), CIO (chlorine residue) and COD (chemical oxygen demand). A summary of the purpose of these tests is shown in the table below.










Using other brands of testing kit has different methodology.  I received the most number of questions regarding the use of API gH test kit from my customers because the test kit expires after two years it has been manufactured.  Expired test kit does not change color that much.  The manufacturing lot number of the test kit is printed on the top of the bottle just over the label and the last 4 numbers will be the month and year it was bottled. If it’s over 2 years or so, it is expired and colors do not develop properly. Please see this video to see how the color really changes from orange to green.


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