4. Temperature, pH, KH and GH

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Author : David Bogert

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The water fish swim in is very important, obviously. But it is not nearly as important as people give it credit for. The chemistry of the water, the pH, the hardness and the salts contained in the water, are just not very important to the well-being of the fish. Most tap water between a pH of 6.5 and 8.5 is fine for all fish. Add conditioner if the water had chlorine in it and you’re good to go.

Read on only if you are a nerd like the author.

Plastic Plants and Parrot Fish
Plastic Plants and Parrot Fish

Myths About Water

There are many myths about the water in which aquarium fish live. Some of these myths are:

  • At least 50% water changes should be done once a week.
  • It’s dangerous to the fish to “chase” pH with chemicals.
  • High pH (>7.5 pH) is dropped by using organic materials such as almond leaves, beech leaves, oak leaves, peat, and/or driftwood.
  • Fish will have their lives shortened if put in a pH different than their native waters.
  • Fish from the Blackwater Amazon will suffer in water with a high pH.
  • The hardness (GH and KH) of the water is very important to the fish.
  • Fish will have their lives shortened if put in a water hardness different than their native waters.
  • Rapid changes (in seconds) in water parameters (pH, hardness and/or temperature) can damage or kill freshwater fish.
  • Temperatures need to be closely held for healthy fish and heaters are an absolute necessity in most homes.
  • Stability in aquarium parameters (temperature, pH, hardness) over hours or days is important.
  • Nitrates going above 10, 20, 40 or even 80 ppm will shorten the life of an adult fish.
  • Ammonia levels at some level below 5 ppm or nitrite levels below 1 ppm are detrimental in any way to fish at a pH of 7.
  • Ammonia levels at 5 to 10 ppm or nitrite levels at 1 ppm to 5 pm are very toxic to fish at a pH of 7.
  • When shipped fish are un-bagged, they should be gradually acclimated to their new water chemistry.
  • Water that has been run through a water softener is bad for fish.
  • Water changes remove built up toxins and fish hormones in the water.
  • Water changes are bad because they cause variation in the water parameters.

ALL these myths are simply false

Picture of an aquairum fish Ruby Red Roter Kaiser
Ruby Red Roter Kaiser

Temperature, pH, GH and KH in Depth

A chart is probably the easiest way to condense most of the water parameters into one:

LocalityIdeal temperatureIdeal temperatureAcceptable temperatureAcceptable temperatureAcceptable excursionAcceptable excursion
African rift75-80°F24-27°C70-90°F21-32°C65-95°F18-35°C
Most fish70-85°F21-29°C70-90°F21-32°C65-95°F18-35°C
LocalityNative pHAcceptable pH in aquariumAcceptable excursion
African rift7.5-8.56.5-8.55-9
Most fish6.5-8.56.5-8.55-9
TDS needs to be above 60
KH and GH are not important
Tropical fish freshwater pH
Aquarium pH, GH, and KH for BEGINNERS​

Click on this link for more in depth discussion of this point:

4.1. Importance of Water

Temperature should be in the proper range for the fish species, with the understanding that these ranges are quite broad, 70 to 90°F (21-32°C) being typical. Note that some fish require very specific temperatures for breeding. Click on this link to see this discussion:

4.2. Aquarium Temperatures

Tropheops chilumba
Tropheops chilumba

The water needs to be as bacteria free as possible for the best health of ALL fish. This requirement is very important but rarely even mentioned or discussed. Click on this link for this discussion:

4.3. Free Floating Bacteria

The pH of the water is not very important. The only time fish can get in trouble is if a fish from a water with some hardness and some salts is put in very soft acid water. There are also some fish such as fish from blackwater which require a very specific pH ranges to breed. Click on this link for this discussion:

4.4. Aquarium pH

Maylandia estherae OB Hybrid
Maylandia estherae OB Hybrid

Hardness is of little consequence except in that some hardness (dKH>2) stops a “crash” (high ammonia levels) or “old tank syndrome” from occurring. And some dKH is needed during cycling. Also some fish require very specific GHs in order to successfully breed. Click on this link for this discussion:

4.5. Water Hardness

Salts are no important so long as most fish have a little. If one has RO water they take on more significance. Total dissolved solids (i.e. the amount of salts) should be above 60 ppm. Click on this link for this discussion:

4.6. Salts in the Water

One myth to be dispelled here is that fish which have been bred in captivity are somehow more resistant to high or low pH and hardness excursions. The science says this isn’t true. ALL fish are equally immune to pH, temperature, KH and GH excursions. Breeding has nothing to do with it. Click on this link for this discussion:

4.7. Fish Tolerance to pH

Cyphotilapia Frontosa Kansombo
Cyphotilapia Frontosa Kansombo

Another myth to dispel is the concept of “stability” in water parameters. The myth is that it is vital to keep a fish from having a rapid swing in pH or a rapid swing in temperature. The science says this isn’t true. Click on this link for this discussion:

4.8. Stability is Not Important

And the method of adding shipped fish to the aquarium has changed recently. Most experts recommend the “cut-pour-plop” method. Click on this link for this discussion:

4.9. Un-bagging Fish

And some aquarium “experts” push “ORP” or “Redox” as being very important in the aquarium. It is not important. We examine that in this link:

4.10. ORP and Redox in the Aquarium

Then there are some “tank syndromes” where some of the water parameters, including water clarity, are diagnostic. “Old tank Syndrome”, ” New Tank Syndrome” and “Sick Tank Syndrome” are covered in this article:

4.11. Tank Syndromes

There are also a series of chemicals found in water which many consider “toxins”. These are covered in these links:

5. Ammonia, Nitrite, Nitrate and Chlorine

5.2. Safe Ammonia Levels

5.3. Safe Nitrite Levels

5.4. Safe Nitrate Levels

5.5. Chlorine and Chloramine

Pterophyllum scalare Veiltail Platinum Angelfish
Pterophyllum scalare – Veiltail Platinum Angelfish