Water Parameter

Parameters in Sea Water Aquaria (Reef tanks)

To ensure organisms in an aquarium best livelihood some parameters (chemical and physical values) should be in a defined range. This overview shows the most important parameters with their optimum range for tropical reef tanks. In case of overshooting and undershooting of the limits directives are given.




Most of the water parameter can be moved to an optimum rage by using appropriate technology or additives.

What to do if a value is not correct?

If a value is clearly overshooting or undershooting the optimum this may have some causes:

  • During the test procedure you have not worked cleanly or you have made a mistake:
    • repeat the test and read the instruction manual if necessary
  • The test is not working properly and shows wrong values:
    • check the test with a standard (a solution with a defined concentration of the wanted substance)
    • purchase a new test, maybe another brand
  • The test is not suitabel for sea water:
    • only tests with explicit written ability for sea is useable
  • Check your sample by a professional lab
  • Record a test report. Only with enough data you may recognise slowly changes of a parameter. A grafic analysis e.g. with an office program like Excel is very useful to differ between outlier and trend.

The optimum range of some parameters

Before acting first think your procedure over: is a change necessary? Each change should be done very carefully and slowly - except at acute danger of toxication. The below listed methods are recommendations and are not the golden path to success. Instruction manuals and safety advises of units and chemicals must be followed in any case
Children should never reach chemicals and test reagents.

Short overview

Parameter Abbreviation Minimum Range Maximum
Ammonium + Ammonia NH4+ + NH3 ( NHx) -  0.1 mg/l
Calcium  Ca2+  400 mg/l 450 mg/l
Density at 25°C   \rho (Rho)  1.022 kg/l  1.024 kg/l
Electrical Conductivity at 25°C Cond, κ (Kappa)
 50 mS/cm  52 mS/cm
Iron Fe  0.01 mg/l  0.1 mg/l
Yellow Substance / Tannins
 -  -  visible yellowish water
Iodine I  0.02 mg/l
0.06 mg/l
Karbonate Hardness
Alkalinity
KH

7°dKH
2.5 mmol/l
12°dKH
4.3 mmol/l
Magnesium Mg 1200 mg/l 1500 mg/l
Nitrate  NO3-  5 mg/l 20 mg/l
Nitrite  NO2-  -  0.1 mg/l
pH value
- 8.0  8.5
Daily pH oscillations
Δ-pH value - 0.3
Phosphate PO43- 0.05 mg/l 0.2 mg/l
Redoxpotential / ORP
E 250 mV 350 mV
Salinity / Salt concentration
S 33 g/kg 37 g/kg
Oxigen O2  90% -
Strontium  Sr2+  8 mg/l  10 mg/l
Temperature T 22°C  27°C (30°C)

mg/l is nearly the same as ppm

 

Alkalinity / Carbonate Hardness / KH / Acid Capacity / Acid Binding Capacity / Buffering Capacity

Optimum Range 7°dKH                         12°dKH
2.5 mmol/l              4.3 mmol/l

Sources
  • Water change with a sea salt containing high amounts of alkalinity
  • manually supply of alkalinity additives as fluid or powder (Balling method)
  • automatically supply of fluid alkalinity additives (Balling methode)
  • CO2 driven chalk reactors (lime reactors)
Sinks
  • Incorporation by lime-forming organisms as corals, escpecially hard corals
  • natural precipitation that forms solid calcium carbonate (the higher the pH the more will be precipitated); the precipitations are skimmed off or settle down in the pore space of the ground
Features One of the most difficult chemical subjects in the aquaristic; a lot of information in the net or in articles are wrong. The terms alkalinity / carbonate hardness / KH / acid capacity / acid binding capacity / buffering capacity mean essentially the same - only the scales differ. In the European area the term carbonate hardness (KH) is used, in the North American region alkalinity is preferred.
You only must know: the higher the alkalinity the more stable is the pH value.
Detailed Information Info: Total hardness / Alkalinity / Magnesium / KH / Acid capacity - an overview
Info: Methods for rising soluble calcium and hydrogen carbonate (alkalinity) in sea water
Info: Dosing lime water "Kalkwasser"
Info: Sodium Hydrogen Carbonate in the KWR
Info: How to work with Care Products? - How much Chemistry do I need?

Ammonium / Ammonia

Optimum Range
0                                 0.1 mg/l
Sources Ammonia is formed as a waste-product that is secreted through the gills. The higher the fish load and the higher the food input, the higher is the ammonia secretion by the animals.
Sinks In a well running aquarium (after the start-up time) toxic ammonia is oxidized immediately over nitrite to the relatively nontoxic nitrate by nitrifying bacteria. The toxic ammonia is converted to a harmless substance.
Immediate actions in case of an ammonia intoxication:
  • large water change, ca. 50%
  • ammonia detoxifier: e.g. Toxic-Ex
  • slowly lowering of the pH of maximum 0.5 steps
Features Ammonium (nontoxic) and ammonia (toxic) are in a pH, temperature and salinity depending balance. Because of the high pH in sea water (compared to fresh water aquaria) the equilibrium is on the side of ammonia. With conventional "ammonium" tests (they measure the sum of ammonia and ammonium) the concentration should be "non-detectable".
Free ammonia calculator
for calculating the toxic part of ammonia/ammonium

 

Calcium

Optimum Range 400 mg/l                     450 mg/l

Sources

The natural reef is supplied with calcium by currents from the deep sea. In the aquarium there are following suitable methods:

Sinks
  • incorporation of calcium by calcium carbonate forming organisms like corals, especially hard corals
  • natural precipitation that forms solid calcium carbonate (the higher the pH the more will be precipitated); the precipitations are skimmed off or settle down in the pore space of the ground
  • too low magnesium concentration that enhances the above precipitation reaction
Features The calcium needs of an aquarium is very different. Fish tanks and aquaria with soft and lether corals need less amounts of calcium. Hard coral tanks may need a manifold of the needs. So a chalk reactor makes sense.
Detailed Information Info: Total hardness / Alkalinity / Magnesium / KH / Acid capacity - an overview
Info: Methods for rising soluble calcium and hydrogen carbonate (alkalinity) in sea water
Info: Dosing lime water "Kalkwasser"
Info: Sodium Hydrogen Carbonate in the KWR
Info: How to work with Care Products? - How much Chemistry do I need?

Currents

Optimum Range

depending on specimen

Sources
  • internal pumps: "Turbelle", propeller pumps or others
  • external flow pumps: closed loop with energy saving pumps
  • wave machine
  • airlift
Sinks
  • compact reef constructions
  • many large corals
  • dirty intake case of the current pump
  • too low pipe diameter of the closed loop system
  • unfavorable geometry of the aquarium
Features Currents are extremely important in reef systems. Without enough currents the animals (corals) get problems to put out waste substances and to get in nutrients. Fish are more fit, because they have to swim a lot in strong currents. In a modern reef tank the currents should be about 10 times the aquarium volume per hour. It is important, too, to make sure that a current is behind the decoration to prevent fouling edges. 
Animals that a not originated from reefs, e.g. sea horses, have their own needs to currents. How much water flow is the best depends extremely on the kept specimen.
Detailed Information  

Density / Salt Concentration / Salinity / Electrical Conductivity

Optimum Range 1.022 kg/l                  1.024 kg/l
33 g/kg (Promill)    37 g/kg (Promill)
50 µS/cm                   52 µS/cm

Sources
  • Supply of salts with the regulare water change with too high concentrations
  • refill a part of the evaporated water with sea salt
  • additives, food
Sinks
  • salt crusts
  • leakage
  • wrong adjusted skimmers
  • water change with water of a lower concentration
Features

You may measure the salt concentration with different methods:

  • measurement of the electrical conductivity (in mS/cm) with a conductivity meter; some units are able to calculate the salinity in g/kg or promill
  • measurement of the refraction index with refractometer (density of salinity are shown)
  • measurement of the density with a araeometer / density hydrometer in kg/l

The salt concentration is very important for running a sea water system. But it is very easy to control (minimum once per month). The salt concentration is the sum of all dissolved salts in the water. It is important that evaporated water is refilled with reverse osmosis water. During the water change the same water volume taking out of the aquarium must be refilled with fresh sea water of the same concentration. In nature most of the reef organisms stay in water with a constant salinity. If you must change the concentration do it slowly. Animals from the Red Sea (40 g/kg) feel good in lower concentrations (35 g/kg), too. In nature these animals are living at the upper limit.

Detailed Information Info: Composition of Sea Water
Info: Salt crusts and lime scale
Info: Water change - Refilling evaporated water

 

Germ Pressure

Optimum Range low                                    high

Sources
  • bad water quality
  • too much food
  • bad quality food
  • new aquaria inhabitants without quarantine
Sinks
  • UV radiation
  • use of ozone
  • antibiotics (use them only in absolutely cases of emergency)
  • well growing corals
  • good currents
  • good circulation with the filter system
Features

Germ pressure is the sum of all bacteria, viruses, fungi and other potetential pathogenic stadia. The higher the germ concentration the higher is the risk of outbreaks. In aquaria the germ pressure is normally higher than in natural untouched reefs. There are allways potential pathogenic organisms in your aquarium (in reefs, too). If a disease occurs of not depends on many factors:

  • number of germs
  • kind of germ (the same germ may have different abilities to induce an illness)
  • stress of any kind:
    • hunger
    • social stress (too many fish, unfavorable composition of the fish species, any hiding places) sozialer Stress
    • bad or highly oscillating water values
    • bad constitution of the fishes
    • bad immune system of the fishes
    • mechanical lesions
If an aquarium system is affected by a persistent and aggressive germ it is sometime necessary to disinfect the complete system with suitabel disinfectiant.
Detailed Information  

 

Iodine / Iodide

Optimum Range 0.05 mg/l                    0.08 mg/l

Sources
Sinks
Features Iodine is important for many reactions in animals, e.g. production of the hormone thyroxine. Also crustaceans need iodine for changing their skin. Iodine must be dosed regularly. The unloaded Iod (I2, e.g. in "Lugol" solution) is more efficient but more dangerous, too, than the loaded ion (I-). The iodide form reacts slowlier but even slightly overdosings will not cause problems.
Detailed Information Info: How to work with Care Products? - How much Chemistry do I need?

 

Iron

Optimum Range 0.01 mg/l                     0.1 mg/l

Sources
  • dosing of iron additives
  • defect iron-containing units like pump impellers with damanged insulation of the magnet
Sinks
  • biological uptake by corals, microorganisms and algae
  • precipitation and oxidation
Features Iron is an important trace element - all organisms need it: corals, fishes, invertebrates, bacteria, algae. In aerobic biotops (e.g. your aquarium) the needed form is iron-II, iron-III is not suitabel for these animals. Iron oxidizes quickly from Iron-II to Iron-III and therefore must be dosed regularly. If the Iron concentration is too high green algae will grow very fast. It is important to you an additive with a protected form of iron-II.
Detailed Information Info: Chelated trace elements: pros and cons
Info: How to work with Care Products? - How much Chemistry do I need?
Info: Materials in Sea Water Aquaristics

 

Light

Optimum Range

too dark                       to bright

Sources
  • natual light (its important to have possibility to shadow the light)
  • artificial light:
    • T8 fluorescent tubes
    • T5 fluorescent tubes
    • metal halids
    • LED- lights (light-emitting diode)
    • plasma lights
All other kind of lights are not suitable.
Sinks
  • to old light source (followin the replacement intervals!)
  • tannins in the water
  • dirty light source
  • covers over the aquarium
  • light is too high over the aquarium
  • inappropriate angel of radiation (wrong reflector)
  • bad lenses of the LEDs
Features
The light is a very complex theme; in one sentence: light intensity, spectrum (composition of wavelengths) and daily time are important. The lighting is not only illuminating the animals - light is essential for corals and others to take their energy for living.
Detailed Information  

 

Magnesium

Optimum Range

1200 mg/l                 1500 mgl/l

Sources
Sinks
  • precipitation reactions
  • intake of animals and algae, especially sea fans and crustose coralline algae (CCA) needs high amounts of magnesium
Features Magnesium is a mineral that is very similar to calcium, but the needs in an aquarium are much lower. Normally a regularly water change is enough to supply magnesium in the right concentration. I some aquaria an additional dosing is important: many CCAs, gorgonians.
If too less magnesium is in the water it is impossible to raise the calcium concentration.
Detailed Information Info: Total hardness / Alkalinity / Magnesium / KH / Acid capacity - an overview
Info: How to work with Care Products? - How much Chemistry do I need?

 

Nitrate

Optimum Range

5 mg/l                          20 mgl/l
ultra-low range ultra-high range

Sources
  • nitrate containing fresh water for water change and refilling of evaporated water
  • nitrate containing sea salt
  • food, plankton, and organic additives
Sinks
  • reverse osmosis units for producing nitrate-free water
  • water change
  • effective skimmer
  • assimilation by algae and corals
  • passively  denitrification: living rocks, deep sand bed, Jaubert system, mud filter system, life sand system
  • actively denitrification: autotrophic (sulfur-nitrate filter) and heterotrophic systems
  • uncontrolled denitrification: "nitrate killer"
Features Nitrate is an end product of the oxidation of ammonia / ammonium done by specialized bacteria called nitrifying bacteria. In the natural coral reef nitrate is only in very small amounts in the water (less than 1 mg/l). In the coral reef aquarium it is important for the nitrogen supply, because of the missing plankton. But in too high concentrations especially in combination with phosphate you get problems with algae, blue-green algae and the growth of hard corals.
Detailed Information Info: Reverse Osmosis Technique for Aquaria
Info: Nitrate - do I need a filter?

 

Nitrite

Optimum Range

                                   0.1 mgl/l

Sources
  •  not complete nitrification
Sinks
  • water change
  • effective skimmer
  • assimilation by algae and corals
  • passively  denitrification: living rocks, deep sand bed, Jaubert system, mud filter system, life sand system
  • actively denitrification: autotrophic (sulfur-nitrate filter) and heterotrophic systems
  • uncontrolled denitrification: "nitrate killer"
Features Nitrite is an intermediate product of the oxidation of ammonia to nitrate. At too high concentrations the blood pigment is blocked and cancer establishing nitro amines are created. The toxicity depends extremely on the pH value of the aquarium water: the more acid the water the more toxic the nitrite. In sea water there is not the danger of intoxication by nitrite - concentrations up to 10 mg/l are possible. Concentrations over 0.1 mg/l shows that the nitrification is not working properly and something happens to the biological filtration.
Detailed Information Info: Nitrate - do I need a filter?

 

Oxygen

Optimum Range

90%                                          

Sources
  • better skimmer
  • ozone use with skimmer
  • remove duff
  • better filter
  • more currents
  • more circulation flow
  • more animals with zooxanthellae and algae
  • algae filter
  • stronger lights
  • oxygen reactor
Sinks
  • supply of organic substances including organic additives
  • use of nitrate killers (uncontrolled denitrification)
  • drop out of the filter system and skimmer
  • compressed ground
  • blocked bio filter
Features The oxygen concentration is normally not measured in seawater aquaria. But many of the seawater animals are sensitive against too low oxygen concentrations. A good skimmer is necessary to prevent a lack of oxygen.
Detailed Information  

 

pH -Value / Δ-pH Value

Optimum Range

                           8.0                                        8.5
           pH-Wert:

                                                             0.3
Δ-(delta)-pH-Wert:     

pH raising
  • dosing of pH raising or alkalinity raising additives
  • use of carbon dioxide by light-depending plants and animals (better growth of these animals and plants needs more carbon dioxide and raises the pH)
  • algae filter (if the lights of the algae filter are operating at night the daily pH oscillations (Δ-pH) will be lower)
  • use of a heterotrophic denitrifying filter
  • lime water dosing (Wilkens method)
  • remove duff
pH falling
  • dosing of pH sinking additives
  • wrong adjustments of a chalk reactor or carbon dioxide reactor COR
  • drop out of the neutralizing stage of a chalk reactor
  • use of a sulfur denitrifying filter
  • drop out of the neutralizing stage of a sulfur denitrifying filter
  • drop out of a skimmer
Features The pH value is a parameter that signs if the water is acid or alkaline. The daily oscillations are called Δ-(delta)-pH value. To prevent damages at fishes the pH should be as constant as possible (a low Δ-pH). You get a very stable pH if the carbonate hardness is high. The inlet of carbonic acid and the missing of aeration (e.g. no skimmer) sinks the pH. The outlet of carbonic acid (e.g. a strong skimmer and photosynthesis) raises the pH. A strong use of carbonic acid by high photosynthesis (algae filter, strong lights) and stripping by a skimmer are ways to raise the pH.
Detailed Information Info: Total hardness / Alkalinity / Magnesium / KH / Acid capacity - an overview
Info: Methods for rising soluble calcium and hydrogen carbonate (alkalinity) in sea water
Info: Dosing lime water "Kalkwasser"
Info: Natriumhydrogencarbonat im Kalkwasserreaktor

 

Phosphate

Optimum Range

0.05 mg/l                    0.2 mgl/l
ultra-low range ultra-high range

Sources
  • phosphate containing fresh water for water change and for refilling the evaporated water
  • phosphate containing sea salt
  • food, plankton and organic additives
  • hoses made of soft-PVC (e.g. some air hoses)
  • coral gravel of bad quality in a chalk reactor
  • additives with bad quality
  • activated carbon with bad quality
Sinks
Features Phosphate is a metabolite of organic substances and is essential in very low concentrations. At too high concentrations especially in combination with nitrate it supports algae and blue-green algae growth and inhibit the forming of the sceleton of hard corals.
Detailed Information Info: Phosphate in Sea Water
Info: How to feed Sea Water Animals

 

Redoxpotential / ORP

Optimum Range

250 mV                        350 mV

Raising ORP
Falling ORP
  • supply of organic substances including organic additives
  • drop out of the filter system and skimmer
  • compressed ground
  • blocked bio filter
Features The ORP is a value that signs if the water reacts in an oxidizing or reducing way. Low ORP shows a bad water quality and high ORP a good water quality. Because it is very complicated to measure the ORP exactly you can only see tendencies. If the ORP is stable or raises it it good, if it is falling something is bad in the aquarium filtration system. In this case you must take care and improve the system: a better skimmer, more currents, water change, delete waste substances, etc.).
The function of nitrate filters can be controlled with the ORP. The value should be between -100 to about -300 mV to ensure a good de-nitrification.
If you measur the ORP do it at the same time of the day, because the ORP depends on the pH-value, too.
Detailed Information  

 

Trace Elements

Optimum Range

too low                        too high

Sources
Sinks
Features High numbers of elements (metals) are toxic in high concentrations but essential in low concentrations for all animals and plants / algae. It is not possible to measure trace elements for hobby aquarists. You must trust the declaration of the manufatures of you must engage a professional analysis lab. If you dose trace elements you only can see some reactions of the animals. Trace elements should not increase the skimming of a skimmer and you should not use solutions with solid precipitations.
Detailed Information Info: Composition of Sea Water
Info: Chelated trace elements: pros and cons
Info: How to work with Care Products? - How much Chemistry do I need?

 

Strontium

Optimum Range

8 mg/l                           10 mg/l

Sources
Sinks
  • natual precipitations
  • uptake by hard corals
Features Strontium increases the growth of hard corals. It is not clear if this element is essential. In too high concentrations strontium is toxic.
Detailed Information Info: How to work with Care Products? - How much Chemistry do I need?

 

Sulfur

Optimum Range

Hydrogen sulfide:
                          cognition limit

Sources
  • capacity overload of the whole filer system with organic substances
  • compressed ground with high organic part
  • inproper use of "nitrate killers"
  • not correctly working nitrate filters
Sinks
  • skimmer, especially with ozone use
  • water currents
  • good aerated bio filter
  • removing fine sediments from the ground
Features Sulfur occurs in seawater as sulfate in high concentration. Only at anoxic condition sulfate is reduced to hydrogen sulfide and the danger of toxication arises.
The elementary sulfur in sulfur-nitrate filters is not soluble in water and brings only problems at wrong adjustments of the filter. If the outlet water of a nitrate filter goes directly into a skimmer the aquarium will not get problems even with a wrong nitrate filter adjustment. The use of ozone increases the oxidation effect.
Detailed Information Info: Nitrate - do I need a filter?
Info: Autotrophic Nitrate Filter - with or without chalk stage?

 

Temperature

Optimum Range

20°C                                 30°C

Optimum: 23-27°C

Raising temperature
  • heater or heat exchanger
  • submersed pumps
  • lighing
  • ambient temperature (room temperature)
  • covered aquaria
  • lighting room over the aquarium without ventilation
Dropping temperature
  • ventilators that blow away the warm and humid air: with high evaporation the temperature will fall about 2-3°C
  • chiller
  • heat exchanger connected to an air condition
Features The temperature must be very constant in tropical reef tanks. With temperature controllers and heater and/or chillers this parameter should be between 23 and 27°C. Check the chiller or heat exchanger before the hot season.
Detailed Information  

Yellow Substances / Tannins

Optimum Range                       visible yellowish

Sources
  • will be formed if bacteria are not able to remove organic substances totally
Sinks
Features Yellow substances, e.g. tannins, are a group of substances that will colour the water yellowish. The light radiation will be lower and the invertebrates like corals will grow less. Especially during the start up of an aquarium yellow substances may occur.
Detailed Information