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PLANTED AQUARIUM CHEMISTRY

The Ultimate Guide

January 23, 2016

BY FRANCES LAI AND KYLE ROBERTSON

Published by Aqua Lab Aquaria at https://aqualabaquaria.com/pages/planted-aquarium-water-testing-chemistry-guide

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Every healthy ecosystem requires a balanced environment. Weekly water tests are invaluable to making sure your aquarium’s levels are in check. Understanding water chemistry and maintaining optimum levels of key nutrients, minerals and other indicators will protect aquatic life and allow the organisms in your care to thrive and radiate. Below are the key parameters to monitor in planted freshwater aquaria.

NUTRIENTS

Ammonia

Nitrite

Nitrate

Phosphate

MINERALS

Carbonate & Bicarbonate (KH)

Calcium & Magnesium (GH)

​

ENVIRONMENTAL INDICATORS

pH​​

Temperature

Use the following information to help you decipher your test results.
Please keep in mind this is a general guide for planted tanks and specific requirements can vary by species. Requirements will also differ for saltwater tanks without coral. Please do additional research before attempting any of the methods outlined here.
Click bold words for more info.

AMMONIA

 

Target Value: 0
Ammonia is a toxic nitrogenous compound released when anything organic breaks down. A large amount of decomposition (e.g. from a carcass or uneaten food) can cause ammonia to spike. Specialized bacteria convert ammonia to nitrite.

TOO MUCH

​

Ammonia levels above 0.25 ppm can suffocate fish, coral and invertebrates in a matter of hours. It is typically present in new tanks and should be cycled out completely before animals are introduced incrementally. Ways to decrease:

​

TOO LITTLE

​

No issues arise from too little ammonia, except when cycling a new tank. Ammonia is necessary at first to fuel the development of bacteria that convert ammonia to nitrite. Ways to increase:

​

  • Add a carbon source (e.g. food, animal waste, or other organic matter) and allow to decompose

  • Start a new tank with nutrient-rich soil such as ADA Amazonia

NITRITE

​

Target Value: 0
Nitrite is a toxic nitrogenous compound produced by bacteria as part of the nitrogen cycle. Specialized bacteria convert nitrite to nitrate.

TOO MUCH

 

Nitrite will reduce the amount of oxygen in fish's blood, and levels above 1 ppm can be lethal in a matter of hours. It is typically present in new tanks and should be cycled out completely before animals are introduced incrementally. Ways to decrease:

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TOO LITTLE

​

No issues arise from too little nitrite.

NITRATE

​

Target Value: 5 - 15 ppm, 25 ppm maximum

The last and least toxic of the nitrogenous compounds, this nutrient is beneficial in small amounts, encouraging plant and algae growth. It is converted from nitrite by specialized bacteria.

TOO MUCH

 

Nitrate levels above 30 ppm can be lethal to aquatic animals in a matter of hours. More nitrate will also lead to more algae growth. Ways to decrease:

  • Dilution via water change​

  • Biological filtration (add heterotrophic bacteria like Prodibio to speed up biofilter development)​

  • Aquatic plants absorb and benefit from nitrate

TOO LITTLE

​

A lack of nutrients will inhibit plant growth. Ways to increase:

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PHOSPHATE

​

Target Value: 0.5 - 1 ppmPhosphate is a nutrient that supports photosynthesis, a vital process for plants.

TOO MUCH

 

Too much phosphate is generally not a concern, but it can promote excess algae growth. Ways to decrease:

​

  • Dilution via water change​

  • Add heterotrophic bacteria like Prodibio

  • Dose liquid carbon (NO3:PO4-X or distilled white vinegar)

TOO LITTLE

​

A lack of phosphate will inhibit plant growth. While dosing potassium phosphate would increase only phosphate, it would usually be better to increase nutrients, like so:​

​

  • Increase feeding

  • Increase bioload

CARBONATE & BICARBONATE (KH)

​

Target Value: 0 - 4 dKH

Carbonate hardness (KH) is determined by the concentration of carbonates and bicarbonates, which provide water with essential buffering capacity. These compounds bind to acids as they appear and neutralize them, thus preventing the pH from becoming more acidic. Carbonate hardness is the main contributor to alkalinity (a parameter used more for reef keeping), so the terms are often used interchangeably.

TOO MUCH

 

Carbonates and bicarbonates will lead to higher pH and reduce the effectiveness of acid buffers. Plus, they will essentially soak up carbon dioxide, binding to the molecules in a way that prevents them from being used by plants. Elevated KH can also cause excessive abiotic precipitation of calcium carbonate from solution, clogging heaters and pump impellers. Ways to decrease:

​

  • Dilution via water change (assuming new water has less or no KH)

  • Wait it out (minerals are constantly being depleted from aquariums)

TOO LITTLE

​

Natural acids are constantly being introduced into aquarium water, and if there is not enough KH to neutralize them, then the water will become vulnerable to dangerous swings in pH. However, if there are other pH buffers in place (a substrate of aqua soil, for instance), then the importance of KH is reduced or even eliminated altogether. Ways to increase:​

​

  • Dose sodium bicarbonate or sodium carbonate

CALCIUM & MAGNESIUM (GH)

​

Target Value: 4 - 8 dGH
General hardness (GH) is comprised mostly of calcium and magnesium, plus trace amounts of other minerals. Calcium is vital for neurological functioning, and magnesium is an important co-enzyme for cells and is necessary for biological functions. In freshwater aquariums, calcium and magnesium deplete at roughly the same rate, so they are measured together as GH.​

TOO MUCH

 

Too many minerals can cause excessive abiotic precipitation of calcium carbonate from solution, which can lead to clogged heaters and pump impellers. Ways to decrease:

​

  • Dilution via water change (assuming new water has less or no KH)

  • Wait it out (minerals are constantly being depleted from aquariums)

TOO LITTLE

​

Low GH will have negative affects on the health and growth of animals. Ways to increase:

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pH

​

Target Value: 6.2 - 6.8 pH
pH is a general environmental indicator that is the cumulative result of many different chemicals and compounds (especially KH). It is a measure of the acidity or basicity of water. Because water enters fish down to their very cells through osmosis, a change in pH of the water causes a change in pH of their blood. Regulating their internal pH takes time and energy, which is why fluctuations are dangerous to fish, even if the pH remains in the recommended range. pH should be maintained constant to a 1/10 precision (e.g. constantly 6.7, not swinging between 6.6 and 6.8).​

TOO MUCH

 

High pH levels are usually the result of high KH, which comes with its own set of consequences. Aside from that, pH levels can be toxic if too high. Ways to decrease:

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TOO LITTLE

​

It is usually a battle to keep pH levels low enough in a planted aquarium. But, pH levels too low can disrupt biochemical reactions. Ways to increase:​

​

  • Dose alkaline buffer

  • Dose sodium bicarbonate or sodium carbonate

  • Decrease carbon dioxide injection or help it escape the water by splashing the surface

TEMPERATURE

​

Target Value: 76 - 80 F (24 - 27 C)
Temperature measures the heat in aquarium water.​

TOO MUCH

 

Heat stress occurs when high temperatures decrease the concentration of dissolved oxygen in water, inhibiting respiration. Heat stress can be fatal. Ways to decrease:

​

  • Blow fan across top of aquarium to facilitate evaporative cooling

  • Use a chilling device

TOO LITTLE

​

All metabolic processes slow down at lower temperatures. Ways to increase:

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