Water Parameters by Species (pH, Hardness, Temp)
Ideal pH, GH, KH, and temperature targets for 22 popular freshwater fish, shrimp, and snails so you can match stock to your tap water and keep a stable tank.
Every fish evolved for a particular kind of water. Some come from soft, acidic blackwater streams, others from hard, alkaline lakes. Matching your stock to your tap water is the single most reliable way to keep healthy fish, because a stable tank that suits its residents beats one you constantly adjust with chemicals. This chart lists target temperature, pH, and hardness for the most popular species.
Quick answer: Most community fish do well at pH 6.5 to 7.5, GH 4 to 12 dGH, and 74 to 80 F. Soft-water fish like cardinal tetras and discus want pH 5.5 to 7.0 and low hardness, while livebearers and African cichlids prefer pH 7.5+ and hard water. One dGH or dKH equals about 17.9 ppm. Aim for stable values over perfect ones, and convert units with our aquarium unit converter.
Water parameters chart by species
Ranges below are healthy keeping targets for adults. GH and KH are in degrees (dGH, dKH). Hit a stable value inside each band rather than a single exact figure.
| Species | Temp (F) | pH | GH (dGH) | KH (dKH) |
|---|---|---|---|---|
| Betta | 76 to 82 | 6.5 to 7.5 | 3 to 12 | 3 to 8 |
| Neon tetra | 70 to 78 | 5.5 to 7.0 | 1 to 6 | 1 to 4 |
| Cardinal tetra | 73 to 81 | 4.5 to 6.5 | 1 to 5 | 0 to 4 |
| Guppy | 72 to 82 | 7.0 to 8.0 | 8 to 12 | 4 to 10 |
| Molly | 72 to 78 | 7.5 to 8.5 | 12 to 25 | 10 to 25 |
| Platy | 70 to 78 | 7.0 to 8.2 | 10 to 20 | 5 to 15 |
| Swordtail | 72 to 79 | 7.0 to 8.2 | 12 to 30 | 8 to 20 |
| Angelfish | 76 to 84 | 6.5 to 7.5 | 3 to 10 | 3 to 8 |
| Discus | 82 to 88 | 6.0 to 7.0 | 1 to 8 | 1 to 4 |
| Goldfish | 65 to 72 | 7.0 to 8.4 | 8 to 18 | 6 to 18 |
| Corydoras catfish | 72 to 78 | 6.5 to 7.5 | 2 to 12 | 1 to 8 |
| Bristlenose pleco | 73 to 81 | 6.5 to 7.5 | 5 to 15 | 3 to 10 |
| Zebra danio | 64 to 77 | 6.5 to 7.5 | 5 to 12 | 3 to 8 |
| Tiger barb | 74 to 79 | 6.0 to 7.5 | 4 to 10 | 3 to 8 |
| Cherry barb | 73 to 81 | 6.0 to 7.5 | 4 to 10 | 2 to 8 |
| Dwarf gourami | 77 to 82 | 6.0 to 7.5 | 4 to 10 | 3 to 8 |
| German blue ram | 78 to 85 | 5.5 to 6.5 | 1 to 6 | 0 to 4 |
| Kuhli loach | 75 to 82 | 5.5 to 7.0 | 2 to 8 | 1 to 5 |
| Harlequin rasbora | 73 to 82 | 6.0 to 7.5 | 2 to 10 | 1 to 8 |
| Cherry shrimp (Neocaridina) | 65 to 78 | 6.5 to 8.0 | 4 to 8 | 1 to 4 |
| Amano shrimp | 70 to 78 | 6.5 to 7.5 | 4 to 14 | 1 to 10 |
| Mystery snail | 68 to 82 | 7.0 to 8.0 | 8 to 18 | 5 to 12 |
pH, GH, and KH explained
pH measures how acidic or alkaline the water is on a scale where 7 is neutral. Most fish tolerate a range, and a steady reading is healthier than a perfectly targeted one. General hardness (GH) is the dissolved calcium and magnesium that fish and invertebrates need for healthy physiology, while carbonate hardness (KH) is the buffer that resists pH swings. A tank with very low KH can crash in pH overnight, so KH is the quiet safety net behind a stable pH. Learn the full picture in our guide to pH in the aquarium.
These three values move together. Hard water with high KH almost always reads alkaline, while soft water with low KH tends acidic. That is why livebearers want hard, alkaline conditions and cardinal tetras want soft, acidic water. Group fish by their water type rather than by looks, and the tank practically maintains itself.
Test Kits for Tracking Parameters
AAwipes 8-in-1 Aquarium Test Strips
$9.96 on Amazon
Quick pH, hardness, KH, ammonia, and nitrate strips.
Match fish to your tap water
The easiest path to success is to test your tap water first, then choose fish that already suit it. If your tap runs hard and alkaline, build around guppies, mollies, platies, swordtails, goldfish, or African cichlids. If it runs soft and slightly acidic, you can keep tetras, rasboras, gouramis, rams, and many catfish with no adjustment. Working with your water instead of against it removes the biggest source of stress and ongoing cost.
When you do need to adjust, move slowly. Crushed coral or aragonite raises GH, KH, and pH gradually, while RO water cut with tap softens and lowers them. Always remineralize pure RO water before use, since fish cannot survive in mineral-free water. Spread changes over several water changes so livestock acclimate.
Plan the rest of your tank
Parameters are one layer of compatibility. Confirm your fish also share a temperature band on the temperature chart, that they get along behaviorally on the compatibility chart, and that your numbers fit the tank on the stocking calculator. Convert dGH, ppm, gallons, and temperatures any time with the unit converter, and find every table at our reference charts hub.
Frequently Asked Questions
What are GH and KH in an aquarium?
GH, general hardness, measures dissolved calcium and magnesium, the minerals fish and snails use for healthy bones, shells, and osmoregulation. KH, carbonate hardness, measures carbonates and bicarbonates that buffer your water and keep pH stable. Both are reported in degrees (dGH and dKH) or in ppm, where one degree equals about 17.9 ppm. Low KH lets pH swing easily, so it matters as much as the pH reading itself.
Should I chase the perfect pH for my fish?
No. A stable pH that sits anywhere near a species range is far safer than constant chemical adjustments aimed at a perfect number. Most commercially raised fish are bred in average tap water and adapt to a steady pH between 6.8 and 7.8. Sudden pH shifts from additives stress fish more than a reading that is slightly off. Focus on stability, and only soften or harden water deliberately for sensitive or breeding species.
How do I find out my tap water parameters?
Test a fresh sample with a liquid test kit, which is more accurate than strips, and also check your water utility report online for hardness. Knowing your tap pH, GH, and KH tells you which fish will thrive with no adjustment. Matching fish to your water is far easier and cheaper than constantly altering water to fit the fish, so let your tap supply guide your stock choices.
Which fish are easiest for hard, alkaline tap water?
Livebearers love hard water: guppies, mollies, platies, and swordtails all thrive at higher GH and KH with pH above 7. African cichlids, goldfish, and many snails also do well. If your tap is hard and alkaline, build around these species rather than fighting your water to keep soft-water fish like cardinal tetras or discus, which need very different conditions.
What is TDS and how does it relate to GH and KH?
TDS, total dissolved solids, measures everything dissolved in the water including minerals, salts, and waste, reported in ppm by a cheap meter. It is a quick general health check rather than a substitute for GH and KH. Shrimp keepers in particular watch TDS closely because it reflects the mineral content their colonies need. For most community tanks, GH, KH, and pH give you the actionable detail.
How do I safely change water hardness?
To soften water, mix in RO or distilled water to dilute minerals, or use peat and botanicals for a gentle drop. To harden it, add crushed coral, aragonite, or a remineralizing product, which also raises KH and buffers pH upward. Make changes gradually across several water changes so fish adjust, and always remineralize pure RO water before use, since fish cannot live in mineral-free water.
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