Water, as it comes out of the tap, has been treated to be safe for human consumption. This means certain additives are present which fish are unlikely to have encountered in their natural habitat and which may adversely affect them. Most people are familiar with chlorine in this respect. Fortunately, the aquatic industry has come up with treatments which nullify many of the additives and so can make tap water more suitable for fishkeeping – something not always appreciated by the local water authorities!
In general, most aquarium fish offered for sale will survive in domestic tap water but for those species that are a little more ‘delicate’ the fishkeeper should know something of how water quality may be defined.
Basically, all natural fresh waters originate as rain but absorb ‘contaminants’ as they fall through the atmosphere, permeate through various soils or flow over differing substrates. These dissolved materials make the water either acid or alkaline, hard or soft.
Moving a fish from an environment with one particular quality of water into another too abruptly will cause it to become stressed and therefore liable to contract disease. A typical example of this is where you may buy a fish in an area using one supply of tap water and take it home where your supply is quite different.
The point was made earlier that freshwater fishes are fairly tolerant to change but this only holds good as long as the change is very gradual, so that the fish can be acclimatized to the new conditions as slowly as possible.
pH levels and water hardness
Acidity and alkalinity form the two ‘halves’ of the pH scale. The whole range is numbered from 0 to 14: 0-7 is acid, 7-14 alkaline, with each unit being ten times the preceding one. Fish from jungle streams generally prefer acidic water as their natural home is full of fallen vegetation which decomposes in the water to give an acidic reaction. Alkaline waters usually turn out to be harder in nature. Jungle waters are likely to be soft, with few dissolved minerals. Central American fish, such as the popular livebearers are found in more alkaline waters as are fishes in Africa’s Rift Valley Lakes, which are just enormous water-filled rocky clefts.
Turning back to domestic supplies, the quality of water from the tap depends on the water’s source which may be many miles away from its eventual distribution point. Water from mountains and lakes is likely to be soft whilst water draining off chalky soils will be much harder.
Altering the condition of water is not too difficult in respect of ‘hardness’; simply diluting hard water with a quantity of known softer water (clear rainwater for instance) will bring down the overall hardness quite easily. Should it be necessary to harden the water more, then using a calcareous (calcium-rich) substrate will do the job gradually without killing the fish in the process. Changing the pH is slightly more difficult, as the degree of water’s inbuilt resistance to pH changes (known as buffering) will obviously vary due to differing basic water qualities from locality to locality, but it can be done. You must ensure that all changes to water quality are made as gradually and over as long a period as possible to avoid stressing the fish.
The importance of researching any fish’s needs before buying it will be reiterated many times. However, you can be caught out as many fish are commercially-bred thousands of miles away from their original, natural habitats. In these cases, the water requirements for the wild fish may not be the same as for the same fish that have been bred for the aquarium. Furthermore, the water parameters at your dealer’s premises are likely to be different again – so, whilst research is all well and good you have to be aware of these possible anomalies.