Every fishkeeper eventually reaches the same realization: most fish deaths trace back to wrong or unstable water parameters. Not disease. Not aggression. Not bad food. Just water that does not match what the animal needs.
This chart covers the ideal parameter ranges for the most commonly kept freshwater species. These are not the survival ranges — they are the ranges where each species thrives, breeds, and shows its best color. There is a difference between “will not die” and “will actually do well,” and this chart targets the latter.
How to Use This Chart
- Temperature is in Fahrenheit. Celsius equivalents are in parentheses where helpful.
- pH is the target range for long-term keeping. Most fish adapt to stable pH outside their ideal range better than they handle frequent fluctuations within it.
- GH (General Hardness) measures dissolved calcium and magnesium in degrees (dGH). Critical for shrimp, livebearers, and shell development.
- KH (Carbonate Hardness) measures buffering capacity. Higher KH = more stable pH. Listed in dKH.
- TDS (Total Dissolved Solids) matters mainly for shrimp keepers. Measured in ppm.
Livebearers
| Species | Temp (°F) | pH | GH (dGH) | KH (dKH) | Notes |
|---|---|---|---|---|---|
| Guppies (Poecilia reticulata) | 72–82 | 7.0–8.2 | 8–14 | 4–10 | Hard, alkaline water preferred; fry need minerals for development |
| Endlers (Poecilia wingei) | 72–82 | 7.0–8.0 | 8–14 | 4–10 | Very similar to guppies; crossbreed freely with guppies |
| Platies (Xiphophorus maculatus) | 70–80 | 7.0–8.2 | 8–15 | 4–10 | Tolerant of higher hardness; good in hard tap water |
| Swordtails (Xiphophorus hellerii) | 70–80 | 7.0–8.2 | 8–15 | 4–10 | Need more swimming space than platies; jumpers |
| Mollies (Poecilia sphenops) | 75–82 | 7.5–8.5 | 10–20 | 6–12 | Hardest water preference of all common livebearers; benefit from salt |
Key takeaway for livebearers: These fish evolved in hard, mineral-rich water. Soft, acidic water causes failed pregnancies, bent spines in fry, and shortened lifespans. If your tap water is soft (GH under 6), add a mineralizer or crushed coral.
Tetras and Rasboras
| Species | Temp (°F) | pH | GH (dGH) | KH (dKH) | Notes |
|---|---|---|---|---|---|
| Neon Tetra | 72–78 | 5.5–7.0 | 2–10 | 1–5 | Softer water for breeding; adapts to moderate hardness for keeping |
| Cardinal Tetra | 75–82 | 4.5–6.5 | 1–6 | 0–3 | Truly soft, acidic water preferred; wild-caught need lower pH |
| Rummy Nose Tetra | 75–82 | 5.5–7.0 | 2–8 | 1–4 | Red nose intensity is a pH/stress indicator |
| Ember Tetra | 72–82 | 5.5–7.0 | 2–10 | 1–5 | Hardy nano tetra; adapts to a wide range |
| Harlequin Rasbora | 73–82 | 5.5–7.0 | 2–10 | 1–5 | Blackwater species in the wild; does fine in neutral community tanks |
| Chili Rasbora (Boraras brigittae) | 72–80 | 4.5–6.5 | 1–6 | 0–3 | Tiny; truly soft water brings out the best red color |
| Celestial Pearl Danio (Galaxy Rasbora) | 68–76 | 6.5–7.5 | 4–10 | 2–6 | Cooler than most tropicals; prefers moderate hardness |
Key takeaway for tetras and rasboras: Most species prefer soft, slightly acidic water. This is the opposite of livebearers. Do not keep cardinal tetras and guppies in the same tank and expect both to thrive — their ideal parameters are fundamentally incompatible.
Bettas
| Species | Temp (°F) | pH | GH (dGH) | KH (dKH) | Notes |
|---|---|---|---|---|---|
| Betta splendens (domestic) | 76–82 | 6.5–7.5 | 3–10 | 2–6 | Stable temperature is more important than hitting an exact number |
| Wild-type Betta (various) | 74–80 | 4.5–6.5 | 1–6 | 0–3 | Wild bettas need softer, more acidic water than pet store bettas |
Key takeaway for bettas: Domestic bettas are adaptable, but they absolutely need warm water. A betta in a 68°F room-temperature tank is a stressed, lethargic betta. A heater is not optional.
Corydoras
| Species | Temp (°F) | pH | GH (dGH) | KH (dKH) | Notes |
|---|---|---|---|---|---|
| Bronze/Green Cory (C. aeneus) | 72–79 | 6.0–7.5 | 2–12 | 1–8 | The hardiest cory; tolerates a wide range |
| Panda Cory (C. panda) | 68–77 | 6.0–7.2 | 2–10 | 1–5 | Prefers slightly cooler water than most tropicals |
| Pygmy Cory (C. pygmaeus) | 72–79 | 6.0–7.2 | 2–10 | 1–5 | Nano species; mid-water swimmer unlike most corys |
| Sterbai Cory (C. sterbai) | 75–82 | 6.0–7.5 | 2–10 | 1–6 | Best high-temp cory; compatible with discus tanks |
| Peppered Cory (C. paleatus) | 64–75 | 6.0–7.5 | 2–12 | 1–8 | Coolwater species; does not belong in heated tropical tanks |
Key takeaway for corydoras: Temperature matters more than most people realize. Peppered corys in an 80°F tank will have shortened lifespans. Sterbai corys in a 68°F tank will be sluggish. Match the species to your tank temperature.
Cichlids
| Species | Temp (°F) | pH | GH (dGH) | KH (dKH) | Notes |
|---|---|---|---|---|---|
| Angelfish | 76–84 | 6.0–7.5 | 3–10 | 2–6 | Soft water for breeding; adapts to moderate hardness |
| German Blue Ram | 80–86 | 5.5–6.5 | 1–6 | 0–3 | Needs warm, soft, acidic water — not a community beginner fish |
| Apistogramma (most species) | 76–84 | 5.0–6.5 | 1–6 | 0–3 | Extremely soft water for breeding; moderate for keeping |
| Kribensis | 75–82 | 6.0–7.5 | 4–12 | 2–8 | Most adaptable dwarf cichlid; sex ratio of fry influenced by pH |
| African Rift Lake (Malawi/Tanganyika) | 76–82 | 7.8–8.6 | 12–20+ | 8–15+ | Hard, alkaline water is non-negotiable for these species |
Key takeaway for cichlids: This family spans the entire parameter spectrum. African rift lake cichlids need the hardest, most alkaline water in the hobby. South American dwarf cichlids need the softest, most acidic. Research your specific species — “cichlid” tells you nothing about water requirements.
Ricefish (Medaka)
| Species | Temp (°F) | pH | GH (dGH) | KH (dKH) | Notes |
|---|---|---|---|---|---|
| Medaka (Oryzias latipes) — all strains | 64–82 | 6.5–8.0 | 4–12 | 2–10 | Extremely adaptable; outdoor keeping above 65°F |
Key takeaway for ricefish: Medaka are the most parameter-tolerant fish on this entire chart. They handle everything from moderately soft to hard water, acidic to alkaline pH, and a massive temperature range. Their weakness is not water chemistry — it is strong current and aggressive tankmates.
Shrimp
| Species | Temp (°F) | pH | GH (dGH) | KH (dKH) | TDS (ppm) | Notes |
|---|---|---|---|---|---|---|
| Neocaridina (Cherry, Blue Dream, etc.) | 65–78 | 6.5–8.0 | 6–12 | 2–8 | 150–300 | Hardy; adapts to most tap water |
| Caridina (Crystal Red, Taiwan Bee, etc.) | 68–74 | 5.8–6.8 | 3–6 | 0–2 | 100–180 | Requires active buffering substrate and RO water |
| Amano Shrimp | 68–80 | 6.5–7.5 | 4–10 | 2–6 | 150–300 | Hardy; brackish water needed for larvae to survive |
| Ghost Shrimp | 65–80 | 6.5–8.0 | 4–14 | 2–10 | 150–400 | Extremely adaptable; often used as feeder shrimp |
| Vampire Shrimp | 74–84 | 6.5–7.5 | 4–10 | 2–6 | 150–300 | Filter feeder; needs flow and suspended particles |
Key takeaway for shrimp: Neocaridina are forgiving. Caridina are not. The GH, KH, and TDS ranges for Caridina shrimp are narrow, and going outside them causes molting failures that kill your colony slowly. If you keep Caridina, invest in RO water and a remineralizer.
Shrimp-safe note: Any equipment that interacts with shrimp water — filters, heaters, air pumps — must be shrimp-safe. Uncovered filter intakes, copper-containing medications, and rapid parameter swings are the top three shrimp killers.
Snails
| Species | Temp (°F) | pH | GH (dGH) | KH (dKH) | Notes |
|---|---|---|---|---|---|
| Nerite Snail | 72–80 | 7.0–8.5 | 6–14 | 4–10 | Needs hard water for shell health; will not breed in freshwater |
| Mystery Snail | 68–82 | 7.0–8.0 | 6–14 | 4–10 | Soft water causes shell erosion and pitting |
| Ramshorn Snail | 68–80 | 6.5–8.0 | 4–12 | 2–8 | Most adaptable snail; breeds in almost any conditions |
| Malaysian Trumpet Snail | 70–82 | 7.0–8.0 | 6–14 | 4–10 | Burrows in substrate; population explodes with overfeeding |
| Japanese Trapdoor Snail | 60–80 | 6.5–8.0 | 4–14 | 2–10 | Cold-tolerant; excellent for outdoor ponds |
Key takeaway for snails: Snails need calcium. Period. If your GH is below 6 and your pH is below 7, snail shells will erode. Add cuttlebone, crushed coral, or a calcium supplement to prevent shell deterioration.
Common Planted Tank Species
| Plant Focus | Temp (°F) | pH | GH (dGH) | KH (dKH) | Notes |
|---|---|---|---|---|---|
| Low-tech plants (java fern, anubias, crypts) | 68–82 | 6.0–8.0 | 3–15 | 2–10 | Almost any parameters work |
| High-tech CO2 planted tanks | 72–78 | 6.0–7.0 | 3–8 | 1–4 | CO2 injection lowers pH; lower KH makes pH easier to control |
| Moss (java, Christmas, flame) | 68–78 | 5.5–7.5 | 2–10 | 1–6 | Prefers cooler water; slows growth above 80°F |
The Parameters That Actually Kill Fish
Not all parameters are equally dangerous. Here is the priority order for monitoring:
- Ammonia — Toxic at any detectable level. The number one killer of aquarium fish. Test weekly.
- Nitrite — Toxic at any detectable level. Indicates an uncycled or crashed filter. Test weekly.
- Temperature — Instability kills faster than wrong temperature. Use a reliable heater and a thermometer.
- pH stability — A stable pH of 7.5 is safer than a pH that swings between 6.5 and 7.0. Stop chasing a “perfect” number.
- GH — Matters most for shrimp, livebearers, and snails. Most other species adapt.
- KH — Matters because it stabilizes pH. Low KH means pH crashes.
- Nitrate — Chronic issue, not acute. Keep under 20 ppm for sensitive species, under 40 ppm for hardy fish.
Stop Chasing Perfect Numbers
The biggest mistake I see from fishkeepers who discover parameter charts is obsessive testing and constant adjusting. A fish that has lived in pH 7.8 for six months is adapted to pH 7.8. Dumping pH-down chemicals to chase 7.0 will stress or kill it.
Stable parameters are always more important than ideal parameters. A tank with a steady pH of 8.0, consistent GH of 14, and zero ammonia is a healthy tank for most species — even those that “prefer” lower pH.
Use this chart for two things:
- Choosing species that match your tap water — instead of fighting your water chemistry to keep fish that need the opposite
- Diagnosing problems — when fish are dying, stressed, or not breeding, check whether your parameters are in the right range for that species
Do not use this chart to justify adding chemicals to force your water into a specific range. Match your fish to your water, not your water to your fish.