Munster Fishkeeping Association

"promoting responsible fishkeeping in Munster"

Aquarium Chemistry

 

You don’t need to have an in-depth knowledge of chemistry to successfully run an aquarium but to understand some basics helps.

Let’s first look at the most important parameters in aquarium water and their importance to the welfare of your fish and plants:

  1. pH

  2. Ammonia_(NH3/NH4+)

  3. Nitrite_(NO2)

  4. Nitrate_(NO3)

  5. Hardness

  1. pH

    2. For those of you who always wondered what the abbreviation actually means, let me shed some light on this. The abbreviation stands for potentia Hydrogenii and means Hydrogen potency or Hydrogen exponent.

    The pH is measured on a scale of 0-15 with 7 deemed as neutral. Anything value below 7 is called acidic and anything above alkaline. Most of common aquarium fish occur in water with a ph of 5.8 and around 9. However, all fish are limited to a pH range where they will thrive. For example a cichlid from Lake Malawi prefers an alkaline pH of around 8 whereas Discus or Angelfish prefer an acidic ph below 7.

    What is actually measured when the ph is tested?

    Essentially the number of H (Hydrogen)+ ions when compared with the number of hydroxile ions (OH-). When a solution has a higher number of H+ ions it is acidic and hence when it has more OH- ions it is alkaline. Water with a neutral pH of seven has the same number of H+ and OH- ions. One last thing to remember is that pH is a logarithmic measurement which means in plain English that water with a ph of 4 has ten times more H+ ions than water with a pH of 5 and 100 times more H+ ions than water with a pH of 6 (10*10). This is crucially important when acclimatising fish to your aquarium water. A pH drop of 1.3 in less than one day can and will result in pH shock in many fish. However going up the pH is scale is easier on them.

    One last bit of trivia, the pH scale was invented by the Danish chemist S.P. Sörensen in 1909 who wanted to know how acidic his beer was. Carlsberg don’t do aquariums but if they did….

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  2. Ammonia (NH3/NH4+)

    3. Ammonia is highly poisonous to fish. Toxicity is temperature dependant but let’s just say under normal circumstance even minute quantities will cause your fish to practice the back paddle. Some fish species will keel over and die at concentration of 0.02mg/l.

    In acidic water ammonia occurs as NH4+ and in water just above a pH of 8 NH3 and NH4+ occur in equal numbers.

    For those interested, here is the formula where you can calculate the relation of NH3 and NH4* ions you have in any water at any temperature:

    NH3 = 0,94412 * NH4 / (1 + 10 ^ ((0,0925 + (2728,795 / (t + 273,15 ))) - pH))

    You should not have any nitrite in a properly cycled tank. Ammonia is broken down in the first stage of nitrification.

    Fish give off ammonia through the gills (if they didn’t they would get ammonia burn and raise the pH in the fish’s blood which will prevent their gills from assimilating oxygen into the blood stream ). NH3 is also produced by decaying plant matter, excrements and left over foodstuff. In water with a ph above 9 you will not find any NH4+. NH3 is less acidic hence ammonia does not play such an important role in marine fish keeping.

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  3. Nitrite (NO2)

    4. The next step in the nitrogen cycle. Bacteria called Nitrosomas convert ammonia into nitrite. Nitrite is not as toxic as ammonia but can still be lethal even in small doses.

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  4. Nitrate (NO3)

    5. By far the least toxic of the three parts of the Nitrogen Cycle. Bacteria called Nitrobacter convert nitrite into nitrate. Even a concentration of 50mg/l is generally not lethal to fish but will stunt growth in most species. Ideally your nitrate concentration in your aquarium should not exceed 25 mg/l.

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  5. Hardness

    6. Hardness is divided into general Hardness (gH) and  carbonate Hardness (KH). Let’s look at carbonate hardness first. It is defined as the number of Magnesium and Calcium ions (hydrogen carbonates) in water. There are several ways of measuring carbonate hardness, the most common one measured by test kits in Europe is °dKH. Where on degree of calcium carbonate equals 10mg/l. To convert this to part per million just multiply by 17.86.Carbonate hardness also defines the ability of water to buffer acids hence a high carbonate hardness equals a high ph. Carbonate hardness can be lowered by adding CO2 to the water or boiling it

    General Hardness is defined as the number of permanent hardness and temperate  (carbonate) hardness. Aside from Magnesium and  Calcium ions it also measure sulphate ions which can not be removed by boiling.

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