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REEF AQUARIUM CHEMISTRY

The Ultimate Guide

January 26, 2018

BY FRANCES LAI AND KYLE ROBERTSON

Published by Aqua Lab Aquaria at https://aqualabaquaria.com/pages/reef-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 marine life and allow the organisms in your care to thrive and radiate. Below are the key parameters to monitor in saltwater reef aquaria.

NUTRIENTS

Ammonia

Nitrite

Nitrate

Phosphate

MINERALS

Carbonate & Bicarbonate (KH)

Calcium

Magnesium

​

ENVIRONMENTAL INDICATORS

pH

Alkalinity

Salinity

Temperature

Use the following information to help you decipher your test results.
Please keep in mind this is a general guide for reef aquariums 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.

TOO MUCH

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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 slowly introduced. Ways to decrease:

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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 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

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: 1 - 5 ppm (to promote coral color and keep algae at bay), 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:

TOO LITTLE

​

A lack of nutrients will reduce algae growth. While this might enhance color, it will also result in coral fragility because coral derive glucose and essential amino acids from algae. Ways to increase:

​

  • Increase feeding

  • Increase bioload

  • Dose potassium nitrate (KNO3)

  • Dose amino acids like AcroPower

PHOSPHATE

​

Target Value: 0 - 0.02 ppm
Phosphate is a nutrient that supports photosynthesis, a vital process to the algae living inside coral.

TOO MUCH

 

Too much phosphate will inhibit coral calcification (growth). Ways to decrease:

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TOO LITTLE

​

A lack of phosphate is usually of little concern unless it corresponds to a lack of nutrients in general. While dosing potassium phosphate would increase only phosphate, it's typically better to increase other nutrients as well by:

​

CARBONATE & BICARBONATE (KH)

​

Target Value: 8 - 10 dKH
Carbonate hardness (KH) is the concentration of carbonates and bicarbonates, which bind to acids and neutralize them. This reaction prevents water from becoming more acidic. The presence of these excellent acid buffers serve as the primary indicator of alkalinity. KH and alkalinity are often used interchangeably.

TOO MUCH

 

High KH can cause tip burning or rapid tissue necrosis in coral, plus excessive abiotic precipitation of calcium carbonate from solution, leading 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

​

Acids are constantly being released into aquarium water in the form of nutrients, so a minimum level of KH is needed to neutralize them. Low KH leads to low alkalinity, which means sudden changes in pH are much more likely when acids are introduced. This can be stressful or even deadly for aquatic animals. Ways to increase:

​

  • Dose sodium bicarbonate or sodium carbonate

  • Dose kalkwasser

CALCIUM

​

Target Value: 420 - 450 ppm
Another fundamental mineral of marine aquaria, calcium is important for neurological functioning and necessary for calcification of coral skeletons.​

TOO MUCH

 

Too much calcium can cause excessive abiotic precipitation of calcium carbonate from solution, leading to clogged heaters and pump impellers. Ways to decrease:

​

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

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

TOO LITTLE

​

Too little calcium will negatively affect the health and growth of marine animals, especially coral. Ways to increase:

​

  • Dose calcium chloride

  • Dose kalkwasser

MAGNESIUM

​

Target Value: 1200 - 1400 ppm
Magnesium, an important co-enzyme for cells, is necessary for biological functions. It's also a minor mineral involved in calcification.​

TOO MUCH

 

High magnesium levels are generally well tolerated in marine aquaria, although further research is required to quantify an upper limit and identify associated consequences. Ways to decrease:

​

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

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

TOO LITTLE

​

A lack of magnesium will have negative affects on the health and growth of marine animals and will inhibit coral calcification. Ways to increase:

​

  • Dose magnesium chloride

pH

​

Target Value: 7.8 - 8.6 pH
pH is a general environmental indicator that is the cumulative result of many different chemicals and compounds (especially alkalinity/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 8.2, not swinging between 8.1 and 8.3).​

TOO MUCH

 

It is usually a battle to keep pH levels high enough in a reef aquarium. However, pH levels can be toxic if too high. Ways to decrease:

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TOO LITTLE

​

Low pH levels can disrupt biochemical reactions and inhibit calcification. The best way to increase pH is to drive out CO2 because it acidifies water.

​

  • Use an algae scrubber as part of your filtration system (algae absorbs CO2)

  • Use a CO2 scrubber hooked up to a skimmer

ALKALINITY

​

Target Value: 8 - 10 dKH
Alkalinity measures water's ability to neutralize acids and maintain steady pH levels. pH is greatly influenced by alkalinity, which also helps to enable coral calcification. Carbonate hardness (KH) is the main contributor to alkalinity, so the terms are often used interchangeably.​

TOO MUCH

 

High alkalinity is usually caused by too many carbonates and bicarbonates (KH), which can lead to tip burning or rapid tissue necrosis in coral, plus excessive abiotic precipitation of calcium carbonate from solution, leading to clogged heaters and pump impellers. Ways to decrease:

​

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

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

TOO LITTLE

​

Low alkalinity can lead to sudden changes in pH which can be stressful or even deadly to aquatic animals. Keep in mind that low alkalinity is usually due to a lack of carbonates and bicarbonates (KH). Ways to increase:

​

  • Dose sodium bicarbonate or sodium carbonate

  • Dose kalkwasser

SALINITY

​

Target Value: 34 - 36 ppt (corresponds to 0.0034 - 0.0036 ppm) or 1.024 - 1.026 SG
Salinity is a general environmental indicator measuring all dissolved compounds, including minerals and nutrients. NaCl is the primary salt that contributes to salinity.​

TOO MUCH

 

As with anything, excess salinity can be toxic. Further research is required to quantify an upper limit and identify associated consequences. Ways to decrease:

​

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

TOO LITTLE

​

Low salinity may lead to kidney failure among fish. However, it can be effective in treating parasitic infections. Ways to increase:

​

  • Incremental water changes with properly salinated water

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, leading to coral bleaching and 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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