For most freshwater community tanks, aim for 0 ppm ammonia, 0 ppm nitrite, nitrate under 20 ppm, a pH between 6.5 and 7.5, and a temperature of 75 to 80°F. KH and GH matter mostly for particular fish, shrimp and planted tanks. Stability counts for more than hitting an exact number: a steady pH of 7.6 is better than one that bounces between 6.8 and 7.4.
Freshwater aquarium water parameters chart #
| Parameter | Target for a community tank | Take action at | Test how often |
|---|---|---|---|
| Ammonia (NH3/NH4+) | 0 ppm | Any reading of 0.25 ppm or more | Weekly; daily in new tanks |
| Nitrite (NO2) | 0 ppm | Any reading of 0.25 ppm or more | Weekly; daily in new tanks |
| Nitrate (NO3) | Under 20 ppm (under 10 for sensitive species) | Above 40 ppm | Weekly, before water changes |
| pH | 6.5-7.5 | Sudden changes of more than a few tenths | Weekly |
| KH (carbonate hardness) | 3-8 dKH | Below 2 dKH, where pH can crash | Every 2-4 weeks |
| GH (general hardness) | 4-12 dGH | Far outside your species’ range | Monthly, or after changing water source |
| Temperature | 75-80°F (24-27°C) for tropical fish | A swing of more than 2°F in a day | Daily glance |
| Chlorine and chloramine | 0 | Any detectable amount | When you change water source or conditioner |
These are ranges most tropical community fish handle well. Fish from very soft or very hard water do better toward the edges, which the species table further down covers.
Why do ammonia and nitrite have to stay at zero? #
Ammonia comes from fish waste and rotting food, and in a cycled tank the filter bacteria convert it to nitrite and then nitrate within hours. Any reading at all means the bacteria are behind. How toxic a given reading is depends on pH and temperature. The University of Florida’s fact sheet on ammonia in aquatic systems explains that the toxic un-ionized form rises with pH, so the same test result is roughly ten times worse at pH 8 than at pH 7. We work through the numbers in ammonia spike in a fish tank.
Nitrite interferes with how fish blood carries oxygen. Extension research on fish ponds notes that chloride helps block nitrite uptake at the gills, which is why some keepers add a little aquarium salt during a nitrite spike (SRAC Publication 462). That’s a stopgap. Water changes and a working filter are the fix.
How much nitrate is too much? #
Nitrate is far less toxic than ammonia or nitrite, and it’s the end product your water changes remove. Under 20 ppm is a comfortable target for most tanks. Research is stricter: a 2005 review in Chemosphere by Camargo and colleagues recommends keeping nitrate-nitrogen at or below 2 mg/L to protect the most sensitive freshwater animals. That’s about 9 ppm on a kit that reports nitrate as NO3. The full breakdown, including the unit conversion, is in safe nitrate level for a freshwater aquarium.
What pH should a freshwater aquarium be? #
Most community fish sold today are farm-raised and adapt to a pH between 6.5 and 7.5. Some groups do better at the ends of the scale. Many tetras, rasboras and discus prefer softer, more acidic water, while livebearers and African rift lake cichlids prefer hard, alkaline water.
Don’t chase a number with pH chemicals. pH-down or pH-up products added to well-buffered water tend to wear off, and the back-and-forth swings do more harm than the pH you started with. If you need a different pH, change the source water (RO water blended with tap, for example) or use a natural buffer like crushed coral for harder water.
KH controls how stable your pH is #
KH, or carbonate hardness, is the water’s buffer against acid. Fish waste and nitrifying bacteria produce acid, and KH absorbs it. When KH runs out, pH can drop suddenly, which is why a neglected tank with low KH can crash overnight. If your tap water is very soft (KH of 1 or 2), regular water changes and a small bag of crushed coral in the filter can keep it from bottoming out.
GH matters for shrimp, snails and some fish #
GH measures calcium and magnesium. Shrimp and snails need enough GH to build shells and molt, and livebearers do better in harder water. Soft-water fish from blackwater rivers prefer low GH.
What water do popular freshwater fish need? #
These are commonly cited ranges. Captive-bred fish are often more flexible than their wild relatives, so ask your breeder or store what water the fish were raised in.
| Fish | Temperature | pH | Hardness |
|---|---|---|---|
| Neon and cardinal tetras | 75-81°F | 6.0-7.0 | Soft |
| Betta | 76-82°F | 6.5-7.5 | Soft to medium |
| Guppies, mollies, platies | 72-80°F | 7.0-8.0 | Medium to hard |
| Corydoras | 72-78°F | 6.5-7.5 | Soft to medium |
| Discus | 82-86°F | 6.0-7.0 | Very soft |
| African rift lake cichlids | 76-82°F | 7.8-8.6 | Hard |
| Fancy goldfish | 65-72°F | 7.0-8.0 | Medium to hard |
| Neocaridina shrimp | 68-78°F | 6.8-7.8 | Medium GH, needs minerals |
Goldfish aren’t tropical fish, and they produce a lot of waste for their size. They need bigger tanks and more frequent water changes than most people expect.
How do you test and track freshwater parameters? #
A liquid master test kit covers ammonia, nitrite, nitrate and pH, and a separate GH/KH kit covers hardness. Strips are handy for quick hardness checks, but many skip ammonia. We compare the two in test strips vs liquid test kits, and explain what each parameter means in aquarium water parameters explained.
Fish Tank Tracker logs ammonia, nitrite, nitrate, pH, temperature and alkalinity (KH, in dKH) and charts each one over time. There’s no GH field, so put GH in the test’s notes. Its built-in target bands were written for reef tanks, so on a freshwater tank ignore the pH and salinity bands and judge pH against what your fish need. The ammonia, nitrite and nitrate bands (zero, zero, and 0 to 10 ppm) fit any tank. The free version covers one tank with a month of history, works offline and needs no account.
Frequently asked questions #
What is the most important water parameter in a freshwater tank? #
Ammonia. It harms fish fastest, and it’s the first number to show when something goes wrong. In a cycled tank it should always read zero.
What pH is too high for freshwater fish? #
It depends on the species. Most community fish are comfortable up to about 7.5 or 7.8, while African cichlids and livebearers do well higher. Sudden changes are the bigger danger, so keep pH steady rather than chasing a number.
Is 40 ppm nitrate too high? #
For hardy fish it’s survivable in the short term, but it’s higher than you want. Increase water changes to bring it under 20 ppm, and aim under 10 ppm for sensitive species, fry and shrimp.
Do I need to test GH and KH? #
Test them once when you set up the tank, and again if you keep shrimp, snails, livebearers or soft-water species, or if you change water source. KH is also worth checking if your pH starts drifting down.