Basic Reef Aquarium Water Parameters Guide
In this guide, we'll discuss the basic marine reef water parameters as they apply to our captive systems. No prior knowledge is assumed or required. Our aquariums are filled with saltwater that where possible contains as close as we can get to natural sea water.
What is Sea Water?
By weight, sea water comprises 96.5% water and 3.5% salt. Many different salts are contained in sea water - some in larger concentrations than others. Even low concentrations can be important to living organisms. Sodium chloride is the main salt constituent but that's not the whole story. What other main salts are in sea water? These include calcium, magnesium, potassium and sulphates. When we buy a bucket of salt for our aquarium we get all of these things in a concentration suitable for our captive system requirements. Replenishment of salts is not an automatic or natural process and hence over time depletion is inevitable. The salt manufacturers' recognise and compensate for this. We have touched upon a fairly important part of being a marine aquarist; we must perform water changes to replenish depleted important minerals and trace elements. Another benefit of water changes is dilution of undesirable nutrients such as nitrates and phosphates.
Let's get straight into the water parameters with an explanation following the tables.
Critical Reef Aquarium Water Parameters
|Parameter||TypicalReef Water||Recommended Reef Aquarium Salt Water|
|Temperature:||variable||25 - 26℃|
|Specific Gravity:||1.025||1.025 - 1.026|
|pH:||8.0 - 8.3||8.1 - 8.3|
|Alkalinity:||7.0 dKH||7.0 - 11.0 dKH|
|Calcium:||420 ppm||380 - 450 ppm|
|Magnesium:||1280 ppm||1310 - 1440 ppm|
|Phosphate:||0.005 ppm||<0.03 ppm|
|Ammonia:||<0.1 ppm||<0.1 ppm|
Other Reef Aquarium Water Parameters
|Parameter||TypicalReef Water||RecommendedAquarium Salt Water|
|Nitrate:||below 0.1 ppm||below 0.2 ppm|
|Nitrite:||below 0.0001 ppm||below 0.2 ppm|
|Silica:||<0.06 - 2.7 ppm||<2 ppm|
|Iodine:||0.06 ppm||0.06 ppm|
|Strontium:||8 ppm||5 - 15 ppm|
|Boron:||4.4 ppm||<10 ppm|
Reef Aquarium Water Parameters Explained
How are reef aquarium water parameters measured?
Normally, water parameters are measured using one of the many test kits that are available in marine and reef keeping shops and online. Some parameters such as calcium, alkalinity and magnesium are easier to measure than others such as iodine and strontium. As a rule, unless you can measure it, don't dose it. The units used are:
|ppm||parts per million - the same as mg/l|
|mg/l||milligrams per litre - the same as ppm|
|ppt||parts per thousand|
|dKH||degrees Karbonathärte (German) or carbonate alkalinity|
|meq/l||milliequivalant per litre|
Conversion Table for Alkalinity Units
|dKH||meg/l||ppm Calcium Carbonate|
Temperature plays an important role in the metabolic rate of living organisms. At higher temperatures oxygen is less soluble. Therefore, relatively lower temperatures cause lower metabolic rates and a higher availability of oxygen.
Specific gravity refers to the ratio of the density of a liquid with reference to the density of pure water and hence it has no units of measure. Therefore when a reef water specific gravity of 1.025 is mentioned, it is 1.025 times more dense than pure water. The temperature of pure water and the sample under test at which this comparison is valid is temperature related. You will often see a temperature mentioned with measuring instruments. Specific gravity shouldn't be confused with salinity that is measured in parts per thousand. Natural sea water has a salinity of approximately 35 ppt.
pH is the measure of acidity or alkalinity and is measured on a scale of 0 - 14. A pH of 7.0 is neutral. Anything below pH 7.0 is acidic (e.g. vinegar at pH 2.0). Anything above pH 7.0 is alkaline (e.g. baking soda at pH 9.0). It should be noted the pH scale is not linear. A pH value of 4.0 is ten times more acidic than a pH value of 5.0. Where possible, fluctuations of pH within the reef aquarium should be avoided as this can lead to undue stress on the living organisms. There is a natural tendancy for the pH to fall in the reef aquarium during the hours of darkness.
Alkalinity is the amount of acid required to reduce the pH to a value of 4.5. Alkalinity is critical to the reef aquarium as corals use "alkalinity" in the creation of their skeletons through the uptake of calcium bicarbonate. Depletion of alkalinity will occur through coral growth. A popular way of maintaining alkalinity is by using a calcium reactor.
Used by many reef corals to form their calcium carbonate skeleton, they obtain calcium from the surrounding water. Calcium depletion in a reef aquarium is a distinct possibility. Replenishing calcium can be done by water changes or dosing with one of the many reef aquarium calcium additives on the market. It should be noted that calcium and alkalinity have a balanced relationship and where possible should approximate the levels in the table below:
Balanced Relationship Between Alkalinity and Calcium
|Alkalinity (dKH)||Calcium (ppm)|
Magnesium plays an important role in balancing calcium and alkalinity. Coral skeletons and coralline algae also incorporate magnesium into their skeletons. If the aquarium's calcium and alkalinity are difficult to maintain, magnesium deficiency may be the cause. Magnesium may be dosed using dolomite in a calcium reactor. Dolomite is calcium magnesium carbonate.
Most test kits measure orthophosphate. Natural reefs by definition are in shallow water where phosphate levels are very low. Unless phosphate is actively managed in the reef aquarium it will accumulate very quickly and lead to growth off nuisance algae and inhibition of calcification. This can sometimes be seen be the lack of coralline algae. Phosphate normally enters the aquarium via the food we feed although phosphate can also be present in new live rock and some coral sands. It is important to wash any frozen food with reverse osmosis/distilled water before putting it into the reef aquarium.
Ammonia is highly toxic to most reef aquarium inhabitants. The only time it should be measurable is during the initial start up and cycling phase of the tank. Most living oraganisms produce ammonia. Fish overstocking, in excess of that which the filtration system can safely process will cause problems.
Much of the nitrate within reef aquaria occurs through feeding. Nirates are a nutrient that cause the growth of undesirable algae. Whilst nitrates are not toxic at the levels found in reef aquaria, they cause an over production of zooxanthellae, the symbitic algae found ion coral tissue. This causes those once brightly coloured corals to go brown. For this reasons stated above, nitrate levels should be kept as low as possble.
Nitrite is the middle phase in the nitrogen cycle that starts with ammonia and ends with nitrate.
Iron is primarily used in the reef aquarium in the growth of plant tissue and is readily taken up by macroalgae (e.g. chaetomorpha, caulerpa etc). An inedequate supply of iron can stunt the growth of macroalgae.
In the reef aquarium many organisms such as diatoms, sponges and molluscs use silica. If there are sufficient numbers of diatoms then there is a ready supply of silica. If not then the system is deficient and you might consider dosing.
Iodine is known to be used by macroalgae species. Whilst there are many iodine forms, two predominate in sea water. These are iodate and iodide. Research has yet to provide full answers as to its use by marine organisms. Regular water changes using a good salt mix should replenish any deficiency.
Whilst in nature there is a certain level of strontium, dosing a reef aquarium without adequate means of measurement could cause more harm than good. Hence regular water changes using a good salt mix should replenish any deficiency.
Boron contributes only a minor fraction of normal sea water's pH buffering capacity. In general, boron is not an important element to control in a reef aquarium.
ORP (oxidation reduction potential)
ORP is a measure of the water properties in the reef aquarium. Monitoring ORP can reveal events such as the death of an organism or something else that is wrong within the system.