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B.K.A. Information pamphlet No.1 1983 H.Casey and R.Cox

Water, to fish as with all other aquatic creatures, is as important as air to humans. Therefore, it is important that aquarists, of whatever capability, should know and have regard to, the water conditions required by their respective charges, in order that they may be successful in keeping and breeding these beautiful fish. It is with this in mind that this document has been produced. Whilst the chemistry of water is a vast subject, this has been kept as simple as possible in explaining the various terms and quantifications.

In simple terms water can be described as hard or soft and acid or alkaline, Usually if water is acid it is also soft and if it is alkaline it is hard,although the two are not directly linked. Whilst rainwater is generally soft, tap water can vary considerably from soft to very hard, depending on which part of the country you live. If your water is obtained in a chalky part of the country it will be hard and if from a peaty area, soft. The term hardness expresses the amount of calcium / magnesium salts which are dissolved in the water. The more salts dissolved the harder the water. This is expressed in terms of degrees of hardness ( Clarke ) or more widely as parts per million - p.p.m. Were there only the Clarke scale of hardness then it would be relatively simple, but we also has the German scale. Care should always be exercised in establishing which scale is being used. Of course if everyone used parts per million in expressing hardness it would be easier, but nothing is ever that simple. The following is a comparison of the relative differences in the scales compared to parts per million:

British degree of hardness = 14.3 p.p.m. German degree of hardness = 17.86 p.p.m.

The British, or Clarke, Scale is hardly ever used now. The German scale is expressed as DH - meaning Deutsche harte ( German Hardness not Degree of Hardness ). The p.p.m. system is used universally throughout industry and scientifically. Whilst Clarke and p.p.m. express hardness in terms of dissolved calcium carbonate (CaCo3), the German system expresses it in terms of dissolved calcium oxide (CaO). Using molecular weight it is relatively easy to convert DH system to p.p.m.

Ca = 40; C = 12; o = 16. Molecular weight of CaCO3 = Ca+C+O+O+O = 40+12+16+16+16 = 100. CaO = Ca + O = 40 + 16 = 56 CaCO3 100 ratio = DDDD = DDD = 1.786 CaO 56 As DH = 100,000 parts of calcium oxide and p.p.m. = 1,000,000 parts of calcium carbonate, 1 DH = 1 part CaO/100,000, = 10 parts CaO/1,000,000. Therefore 1 DH = 10 x 1.786 + 17.86 p.p.m. Therefore DH x 17.86 = p.p.m.

The term used to express acidity or alkalinity is the symbol pH. On a pH scale 7.0 is neutral. All readings below this number are acid and all above are alkaline. It therefore follows that the lower the reading the more acid the solution and the higher the more alkaline.

In so far as killifish are concerned pH readings of between 5 and 8 are usually encountered. Most killies will do quite well within this range but a few must have very soft, slightly acid conditions, to reproduce. Generally speaking it is better to keep killies in hard water as they seem less susceptible to disease than they do when kept in soft, acid conditions. The level of pH can be checked with a meter but this is an expensive piece of equipment. Good results can be obtained with the use of pH paper obtainable from all good aquarists shops and contain full instructions in their use.

Certainly for most species of killifish, whether for breeding or keeping, the best water is rain water. This is easily collected using wood, glass or polythene containers. When collecting it is best to wait for about half an hour after the rain has started in order that dirt in the atmosphere is washed out. In country areas well away from the industrial conurbations this is not so important, but in town it is vital. Even so, in heavy industrial areas the water may be as acid as 3.5 pH but in coastal areas neutral to slightly alkaline. Rainwater collected near the sea should be checked carefully as a high salt content can be found in rainwater blown in from the sea. A golden rule must be to check your newly collected rainwater before using it. Sudden and violent changes in the aquarium can cause shock and death to killies so always change water conditions very slowly.

Having decided upon which of the varying conditions you are going to adopt, be careful to stick to them. Change is only necessary if your fish are not thriving or breeding satisfactorily. If you wish to soften and acidify water then the addition of small quantities of rainwater over a period of several weeks will satisfactorily attain this. Chemicals can also be used but due to the risk involved in their use this is not recommended. Conversely if you wish to harden your water and your tap water is also soft, then the addition of small quantities of lime will achieve this. To determine the hardness of water is rather more difficult but again test kits can be purchased which will give a rough guide. Your local water authority keep a daily check on the chemical content of your water and this information can be obtained by telephoning them. Hard tap water can be partially softened by heavy aeration over a period of a few hours, by boiling or by using a proprietary softener. Softness and acidity can also be obtained by the addition of peat to the water. If left for a period of two to three weeks it will become quite soft and acid and can be syphoned off and mixed with other water until the correct pH and p.p.m. are obtained.

Generally speaking if you use rainwater or tap water, once your fish are accustomed to it they will do well, It is only when changes are made suddenly that things may go wrong. All killies seem to relish a partial water change, about 20% as a rule, once a week and this quite often stimulates breeding. Most will breed within a pH range of 6.4 - 7.4 and a hardness of 20 - 180 p.p.m. So you can see that the range is quite wide. It is only a few species which require conditions on either side of the range.

Most fish relish the addition of a teaspoonful of cooking or sea salt crystals per gallon of water as this tends to prevent the outbreak of harmful bacteria, which could lead to diseases such as velvet.