Ideal water parameters chart by type of tank
Updated on August 26, 2026 · ~7 min read
In a freshwater community: pH 6.5-7.5, temperature 24-27 °C (75-81 °F), ammonia and nitrite 0 ppm, nitrate under 25 ppm, GH 6-12 dGH, KH 3-8 dKH. In a reef: pH 8.0-8.4, 24-26 °C (75-79 °F), salinity ~35 ppt, KH 7-9 dKH, calcium 400-450 ppm, magnesium 1250-1400 ppm, nitrate 1-10 ppm, phosphate 0.02-0.1 ppm.
This is the page to keep open next to your test kits: all the reference values from the other guides, in one place, split by type of tank.
⚠️ These are reference ranges, not prescriptions. Every tank is its own case, and for nearly all of these values stability matters more than the decimal: a steady pH of 7.8 is better than a 7.2 that swings. If something is out of range, correct it in small steps — a fast correction nearly always does more damage than the wrong value.
Freshwater
| Parameter | Tropical community | Planted | Notes |
|---|---|---|---|
| Temperature | 24-27 °C (75-81 °F) | 24-27 °C (75-81 °F) | discus higher, 28-30 °C (82-86 °F); shrimp cooler, 20-24 °C (68-75 °F) |
| pH | 6.5-7.5 | 6.5-7.5 | do not correct it directly: work on KH, CO₂ and water changes |
| Ammonia (NH₃) | 0 ppm | 0 ppm | any value above 0 is a problem in progress |
| Nitrite (NO₂) | 0 ppm | 0 ppm | same |
| Nitrate (NO₃) | < 25 ppm | 10-25 ppm | a planted tank needs it: at zero the plants go into deficiency |
| GH (total hardness) | 6-12 dGH | 4-8 dGH | soft water (discus, neon tetras) 2-6; Malawi 8-15 |
| KH (alkalinity) | 3-8 dKH | 3-5 dKH | it is the pH buffer: at zero, pH dances |
| Phosphate (PO₄) | < 1 ppm | 0.5-1.5 ppm | in a planted tank it is fertiliser |
| CO₂ | — | 20-30 ppm with injection | without injection 3-8 ppm |
| TDS | 200-400 ppm | 200-400 ppm | Neocaridina 150-250; Caridina 100-150 |
| Iron (Fe) | — | 0.05-0.2 ppm | only where you fertilise |
| Potassium (K) | — | 10-30 ppm | tolerated in excess better than iron and phosphate |
| Dissolved oxygen | 6-8 ppm | 6-8 ppm | below ~4 ppm is an emergency |
| Copper (Cu) | 0 ppm with invertebrates | 0 ppm | non-negotiable with shrimp and snails |
Marine and reef
| Parameter | Fish only | Reef | Notes |
|---|---|---|---|
| Temperature | 24-26 °C (75-79 °F) | 24-26 °C (75-79 °F) | |
| pH | 8.0-8.4 | 8.0-8.4 | often low because of the room's CO₂ |
| Salinity | 30-35 ppt | ~35 ppt | SG 1.025-1.026; ~53 mS/cm |
| Ammonia / nitrite | 0 ppm | 0 ppm | |
| Nitrate | < 25 ppm | ~1-10 ppm | corals suffer even at low values |
| Phosphate | < 0.5 ppm | 0.02-0.1 ppm | needs a low-range test |
| KH (alkalinity) | 7-9 dKH | 7-9 dKH | and stable: at most ~1 dKH per day |
| Calcium | — | 400-450 ppm | if it will not come up, check the magnesium |
| Magnesium | — | 1250-1400 ppm | ~3 times the calcium |
| Silicate (SiO₂) | — | < 0.1 ppm | ideally undetectable (diatoms) |
| Dissolved oxygen | 6-7 ppm | 6-7 ppm | salt lowers saturation |
| Redox (ORP) | — | 300-450 mV | a 50 mV drop within hours is worth a look |
| Copper (Cu) | 0 ppm | 0 ppm | never treat with copper in the display tank |
| GH | not measured | not measured | in marine tanks you follow calcium and magnesium |
Brackish
| Parameter | Value |
|---|---|
| Salinity | 5-15 ppt (~1.004-1.011) |
| Temperature | 24-27 °C (75-81 °F) |
| pH | 7.5-8.2 |
| KH | 4-10 dKH |
| Ammonia / nitrite | 0 ppm |
| Nitrate | < 25 ppm |
Salinity must be set to its final value from the start: filter bacteria adapt to the environment they grow in, so changing it after the tank has matured reopens the cycle.
The units, and how they convert
Kits from different brands use different units for the same thing. These are the conversions:
| Quantity | Canonical | Conversions |
|---|---|---|
| Temperature | °C | °F = °C × 9/5 + 32 |
| Alkalinity | dKH | 1 dKH ≈ 0.357 meq/L ≈ 17.9 ppm CaCO₃ |
| Total hardness | dGH | 1 dGH ≈ 17.9 ppm CaCO₃ |
| Salinity | ppt | ppt ≈ (SG − 1) × 1400 · ppt ≈ mS/cm × 35/53 |
| TDS | ppm | ppm ≈ µS/cm × 0.5 |
⚠️ The salinity ones are approximations: the real relationship is not entirely linear and depends on temperature. They are enough to tell where you are, not to compare decimals across different instruments.
Which of these to actually measure
The full list is intimidating, and unnecessary. In practice:
In a new freshwater tank: ammonia and nitrite every 2-3 days, nitrate at the end to confirm the cycle. That is all.
In an established freshwater tank: nitrate before every water change, temperature checked daily by eye, pH/GH/KH once a month. The rest only if there is a problem or if you fertilise.
In a reef: KH once or twice a week (it is the one that moves fastest), calcium and magnesium every one to two weeks, nitrate and phosphate every one to two weeks, salinity and temperature continuously.
Measuring everything every day does not help and is tiring. What helps is writing the results down: most diagnoses are made on the direction a value is moving, not on today's value.
First of all: measure your tap water
There is one measurement worth more than all the others and almost nobody takes it: the one on the water out of your own tap, before setting the tank up. It answers three questions that cost far more later.
What GH and KH you have at home. From this you choose your inhabitants, instead of choosing inhabitants and then correcting the water for years. A tap at 12 dGH and 6 dKH is perfect for a tropical community exactly as it is; at 20 dGH it is worth looking at African cichlids or livebearers, and at 3 dGH at soft-water fish.
Whether it contains nitrate. In many farming regions the tap comes out at 20-40 ppm. Anyone changing 30% of the water weekly and unable to get below 30 ppm in the tank is putting back what they take out: the value the tank converges on is that of the new water, not zero. The only way out, in that case, is cutting with RO water.
Whether it contains phosphate or silicate. Some water utilities add phosphate as a corrosion inhibitor for the pipes. It is one of the least suspected causes of persistent algae in freshwater, and of diatoms that never end in a marine tank.
It is a ten-minute check made once in a tank's life, and it rewrites half the diagnoses that follow.
The three rules that apply to the whole chart
- Ammonia and nitrite do not have a range: they have a value, zero. Everything else is a band.
- The speed of the change does more damage than the value. True for KH, salinity, temperature, pH and hardness. When in doubt, more slowly.
- Before correcting, ask whether it is needed. Tap water at 12 dGH and 6 dKH is perfect for a tropical community exactly as it is. Treating it "to improve it" adds a permanent weekly job and a risk at every water change.
How Gurglee does it
These ranges are Gurglee's catalogue — the same source, so site and app never give two different answers about the same parameter. The app applies them per type of tank, so the same nitrate value comes out in band in a freshwater tank and out of band in a reef, and parameters that are not measured in a given type of tank do not even appear in the list. The bands can be changed for your own tank, and units convert themselves — so a German kit and an American one end up on the same chart instead of two. In "Basic" level the app shows only the essential parameters, and the full 19 arrive with "Expert" level.
Related guides
How to read a liquid test kit without getting it wrong
Liquid test kits go wrong less often than the people reading them: light, background, angle, waiting times, expired reagents and the traps of each individual kit.
Water hardness: GH and KH explained simply
GH and KH are not the same thing: what they measure, which values fish and shrimp need, and how to raise or lower them without doing damage.
Aquarium pH: ideal values and how to correct it
Which pH to hold for each type of tank, why it swings over the day, and why correcting it directly is almost always a mistake. What to do instead.
Calcium, KH and magnesium in a reef: the triangle
Why calcium, alkalinity and magnesium move together in a reef, which values to hold, and why when calcium or KH will not come up the culprit is nearly always magnesium.