By Donna M. Recktenwalt
Water condition and quality are perhaps the most important factors detemining whether our fish are healthy and content. Other factors are essential too suitable temperatures, space, proper food, etc. But if the fish are in poor water they won’t do well period.
Fish can and do adapt to various wataer conditions, but most experts have found that the majority of fish (with the obvious exceptions of the Tanganyikan cichlids and some of the Nothobranchius) do best when the water is moderately soft. The usual breakdown given is: 0-50 ppm, soft; 50-100 ppm, medium soft; 100-200 ppm, medium hard; 200-300 ppm, hard; and 300+, very hard.
In general, very hard water is tough on most fish; preferable is the range from soft to medium hard. Most killifish do quite well in this range, but many killikeepers have found that their local water conditions can be improved by adding softer water to that they get from the tap.
Water softener water is not readily encouraged for aquarium use, but many aquarists use it without apparent ill effects.
“I keep, raise, and breed my Aphyosemions in soft water (1/2 tap and 1/2 distilled) and have done this for years,” says Al Anderson. “I suppose that since these fishes are reputedly from rainy forests, soft water would be the best. However, the bottom spawners, especially the Notho’s, I keep in just plain tap water.” To some extent, the changing water quality as their ponds dry up may help trigger spawning in the annual fishes.
From another point of view: “I feel the ‘soft water myth’ … has probably frightened off scads of aquarists.. Basically there are only two fish I know of that actually required soft water, the discus and the neon tetra,” says Roger Sieloff. Tetras in general fare better in soft water, and Epiplatys annulatus supposedly do better in it. However, Roger reports that he has kept E. annulatus in hard Indiana water and the fish survived, plus “most of the Aphyosemions I’ve kept did alright in ordinary unsoftened tap water.” Rivulus species are hard water tolerant, in his opinion, and pupfish require hard water, including soda, salt, and perhaps borax.
Several acceptable methods of “softening” water are available. Among them are the use of distilled water, reverse osmosis water, rainwater, and peat. For individual tanks with appropriate filtration, adding peat, black peat granules, or a softening pillow to the filter compartment can help bring down the pH and the hardness.
Distilled water is fine for those with limited aquaria, but can become pricey when more than a few small tanks are involved.
Rainwater can be an inexpensive option, if you have a way to collect it and can be assured of its cleanliness. More than one aquarist positions collecting containers beneath their home’s downspouts. In general, allow the rain to run off for a time before collecting, to allow any contaminants to wash away. Then collect the water and store it for use. For small amounts, clean glass or plastic jugs work well; for larger amounts, poly barrels with appropriate plumbing may be in order.
Reverse osmosis units are a reasonable answer if your needs are for moderate or significant amounts of water. These use membranes to filter out all minerals and contaminants, but for small operations are often too expensive.
But not all aquarists face the problem of having to soften hard water. Some find that they have to harden soft water. This can be simply accomplished by using limestone in your tank. Limestone, which is often used for Rift Lake cichlids, can be added as pieces for decoration, as pea sized gravel for substrate, or in filter inserts. Other possibilites are to use crushed coral, crushed oyster shell, or dolomite in similar fashion. Dolomite requires occasional replacement or thorough drying to retain its effectiveneses. The degree of hardness that the additives make depends on the fineness of the gravel, the pH of the water, and the amount of dissolved CO2. Eventually, any of these rocks will become inactive due to a layer of insolubole CaPO4 which forms on the surface, the result of phosphates in fish food.
— GCKA Newsletter, November 1997