Reading your local water report

Where the report is

Water utilities in the United States publish an annual water quality report, usually called a Consumer Confidence Report. It is normally on the utility's website, and it is often posted or emailed to customers once a year. Search for your utility's name with "water quality report" and it will be the first result.

Hardness is not always in it, because it is not a health contaminant and is not required to be reported the way regulated substances are. If it is missing, telephone the utility and ask for the hardness of the supply to your address. They will know, and they are used to the question.

If you are on a private well, there is no report. Test it yourself, and test it more than once across a year — well chemistry moves with rainfall in a way that mains supply does not.

The units, and how to convert them

Hardness is reported in whichever unit the utility prefers, and aquarium species data is normally in degrees of general hardness. Three units cover almost everything you will see:

• mg/L or ppm as calcium carbonate — the usual utility unit.
• Grains per gallon (gpg) — common in the United States, especially on water softener paperwork. One grain per gallon is about 17.1 ppm.
• dGH, degrees of general hardness — the aquarium unit. One dGH is about 17.9 ppm.

The two conversion factors are close enough together that a useful shortcut falls out: grains per gallon and dGH are very nearly the same number. Ten grains per gallon is roughly ten degrees. To go from ppm, divide by about eighteen.

For orientation, the classification US water agencies commonly use runs: soft below 60 ppm, moderately hard 61 to 120, hard 121 to 180, and very hard above 180. In aquarium units that is soft below about 3 dGH and very hard above about 10.

GH and KH are different things

General hardness (GH) is dissolved calcium and magnesium. It is what species data means by "hardness", and it is what livebearers and snails need for shells and skeletons.

Carbonate hardness (KH) is the carbonate and bicarbonate content. It is the buffer: it resists changes in pH. A tank with low KH can swing pH quickly and unpleasantly; a tank with solid KH is stable.

They usually rise and fall together in tap water but they are not the same measurement, and KH is the one that explains most sudden pH problems. If your pH is unstable, look at KH before you look at anything else.

Testing pH properly

Water arriving under pressure carries more dissolved carbon dioxide than it will hold at rest, and carbon dioxide depresses pH. Test a glass straight from the tap and you will get a reading that does not represent the tank at all.

Draw a sample, leave it out for twenty-four hours, then test it. Compare that to a reading from the tank itself. A gap between the two tells you something in the tank — substrate, rock, driftwood, or the fish load — is moving the chemistry, which is worth knowing before you blame the supply.

The report is an average, and your house is not

The published figure is a system-wide value, often an annual average across sources. Several things change it before it reaches your tank:

• A water softener. This is the big one. A softener exchanges calcium and magnesium for sodium — GH falls sharply, but the water is not "soft water" in the sense a cardinal tetra means. KH may barely move, and the added sodium is not something soft-water species evolved with. Many keepers plumb an unsoftened tap for the aquarium.
• Seasonal source switching. Utilities blend sources and the mix changes; hardness can differ between summer and winter.
• Your plumbing. Copper pipework matters if you keep shrimp, which are killed outright by copper-based medications and are sensitive generally.

So use the report to know roughly where you stand, and a test kit to know exactly.

Chlorine and chloramine

The report will say which disinfectant your utility uses, and the difference is practical. Chlorine gasses off if water stands. Chloramine does not, and it must be neutralised with a dechlorinator that handles it — which also releases ammonia that the tank's bacteria then deal with. Do not rely on standing water overnight if your supply is chloraminated.

Match the fish to the water, not the water to the fish

This is the conclusion the whole exercise is for. Chasing a target pH with bottled chemicals produces instability, and instability is worse for fish than a number slightly outside their published range.

Hard alkaline tap water is a good home for guppies, endlers, platies, mollies, nerite and mystery snails, and boesemani rainbowfish. Mystery snails in particular need hard alkaline water or the shell pits and erodes from the tip down. Soft acidic water suits cardinal tetras, chili rasboras, German blue rams and discus.

Some fish barely care. Farmed neon tetras are far more adaptable than their wild blackwater origins suggest, and stability matters more to them than hitting a target. Kribensis tolerate a remarkably wide pH range for a dwarf cichlid, which is why they survive in tap water that kills rams.

The combination worth avoiding is the one that looks harmless on a shop shelf: hard-water and soft-water species in the same tank. A boesemani rainbowfish wants exactly what a cardinal tetra does not, and one of them will be permanently outside its range.

If you genuinely must change the water, the honest route is reverse osmosis water remineralised to a chosen target, mixed with tap water to taste. It is more work and more equipment than most people expect, and it is far more stable than dosing a display tank with pH adjusters.