Water Parameters Cheat Sheet

The single most-referenced document for any serious fishkeeper. This is the quick lookup for water parameters — target ranges, what they mean, species-specific preferences, and how to troubleshoot when things go off. Bookmark this page; you'll return to it regularly.

At a glance: how often to test

When	What to test	Why
While cycling a new tank	Ammonia, nitrite and nitrate, every couple of days	The readings are how you know where the cycle has got to
Weekly, in an established tank	Nitrate — and ammonia and nitrite if anything looks off	Nitrate is the one that climbs on its own between water changes
After any change	Ammonia and nitrite	New fish, a filter clean, a heater failure or a big water change can all disturb the colony
When something looks wrong	Everything, before you treat anything	Many "diseases" are water quality, and a test costs nothing but a few minutes

Two of the six have no acceptable range at all. Ammonia and nitrite must read zero — any reading is a signal to act, not a number to tolerate.

The Six Critical Parameters

Every aquarium keeper needs to monitor:

Parameter	Tests	Healthy Range (Most Tanks)	What It Means
Temperature	Thermometer	72-78°F (22-26°C)	Heat for tropical fish; affects metabolism
pH	Liquid test	6.5-7.8	Acidity/alkalinity; matters for species choice
Ammonia (NH₃)	Liquid test	0 ppm	Toxic waste from fish/decay; must be zero
Nitrite (NO₂)	Liquid test	0 ppm	Intermediate cycle product; must be zero
Nitrate (NO₃)	Liquid test	<20-40 ppm	End cycle product; can build up
GH (general hardness)	Liquid test	4-12 dGH typical	Dissolved Ca/Mg minerals

Other parameters matter sometimes:

Parameter	When to Test	Healthy Range
KH (carbonate hardness)	If pH unstable, planted tanks	3-10 dKH
TDS (total dissolved solids)	RO water, shrimp keeping	150-250 ppm typical
Phosphate (PO₄)	Planted tanks, algae issues	0.5-2 ppm
CO₂	High-tech planted tanks	20-30 ppm

The four core aquarium water readings shown as ranges: temperature 72 to 78 Fahrenheit, pH 6.5 to 7.8, ammonia and nitrite at zero with any reading a problem, and nitrate under 20 to 40 ppm — Two of the four have no acceptable range at all. The other two are bands to sit inside, not targets to hit exactly.

Quick Species Reference

Target parameters by species group:

Hardy Beginner Fish (Wide Tolerance)

Guppies, platies, mollies, swordtails (Livebearers):

Temp: 72-82°F
pH: 7.0-8.2 (prefer slightly alkaline)
GH: 8-20 (prefer hard water)
Nitrate: <40 ppm

Goldfish:

Temp: 65-75°F (cool water!)
pH: 7.0-8.0
GH: 6-20
Nitrate: <40 ppm

Danios (zebra, leopard, pearl):

Temp: 68-78°F
pH: 6.5-7.5
GH: 5-15
Nitrate: <30 ppm

Tropical Community Fish

Tetras (neon, cardinal, ember, glowlight):

Temp: 74-80°F
pH: 5.5-7.0 (prefer soft acidic)
GH: 1-8 (prefer soft)
Nitrate: <20 ppm

Corydoras catfish:

Temp: 72-78°F
pH: 6.0-7.5
GH: 2-12
Nitrate: <30 ppm

Rasboras (harlequin, chili, ember):

Temp: 73-80°F
pH: 6.0-7.5
GH: 2-10
Nitrate: <20 ppm

Gouramis:

Temp: 74-82°F
pH: 6.0-7.5
GH: 4-10
Nitrate: <30 ppm

Demanding Species

Discus:

Temp: 82-86°F (warm!)
pH: 5.5-6.5 (acidic)
GH: 1-5 (very soft)
TDS: <200 ppm
Nitrate: <10 ppm

Wild-caught tetras and apistogramma:

Temp: 76-82°F
pH: 5.0-6.5
GH: 1-5
TDS: <150 ppm

Crystal shrimp (Caridina):

Temp: 68-76°F (cool)
pH: 5.8-6.8
GH: 4-6
KH: 0-2
TDS: 100-150 ppm

Cherry shrimp (Neocaridina):

Temp: 65-80°F (very wide)
pH: 6.5-8.0
GH: 6-12
KH: 2-5
TDS: 150-250 ppm

African Cichlids

Lake Malawi (mbuna, peacock):

Temp: 76-82°F
pH: 7.8-8.6 (alkaline!)
GH: 12-20 (very hard)
KH: 10-18

Lake Tanganyika:

Temp: 76-82°F
pH: 8.0-9.0
GH: 15-25
KH: 12-20

Parameter-by-Parameter Detail

Temperature

Most tropical fish: 72-78°F (22-26°C) Cool water (goldfish, hillstream loaches): 65-72°F Warm water (discus, some gouramis): 80-84°F Brackish: 75-82°F Saltwater (reef): 75-78°F (stable!)

Tip: Stability matters more than the exact number within range. Fluctuations of 4°F+ stress fish.

pH (Acidity/Alkalinity)

Below 6.0: Very acidic — only specialty soft-water species
6.0-6.8: Soft acidic — many wild tetras, discus, apistogramma
6.8-7.2: Slightly acidic to neutral — most community fish
7.2-7.8: Slightly alkaline — livebearers, many community fish
7.8-8.5: Alkaline — African cichlids
Above 8.5: Very alkaline — limited species, possible problem

Tip: Stable pH matters more than chasing a specific number. Don't mess with pH unless necessary.

Ammonia (NH₃)

Always 0 ppm in established tank.

0.25 ppm = stressed fish, immediate action needed
0.5+ ppm = toxic, water change immediately
1+ ppm = emergency, fish dying possible

Source: fish waste, decaying food, dead fish/plants. Indicator of cycling problems or overstock.

Nitrite (NO₂)

Always 0 ppm in established tank.

0.25 ppm = mini-cycle happening, monitor closely
0.5+ ppm = toxic, water change needed
1+ ppm = emergency

Source: bacterial conversion from ammonia. Indicates cycle disruption.

Nitrate (NO₃)

Healthy range: <20 ppm (excellent), 20-40 ppm (acceptable), >40 ppm (high), >80 ppm (problematic)

Source: end product of nitrogen cycle. Builds up between water changes. Reduce via: water changes, plants, less feeding.

GH (General Hardness)

Dissolved calcium and magnesium minerals. Measured in dGH or ppm.

0-4 dGH (0-70 ppm): Very soft — for soft-water species
4-8 dGH (70-140 ppm): Soft — wide compatibility
8-12 dGH (140-210 ppm): Medium-hard — community fish, livebearers
12-18 dGH (210-320 ppm): Hard — African cichlids
18+ dGH (320+ ppm): Very hard — only specialty hard-water species

Tip: GH affects plant growth and snail shells. Most plants prefer 4-12 dGH.

KH (Carbonate Hardness)

Buffering capacity — resistance to pH changes. Measured in dKH.

0-2 dKH: Very low — pH unstable, use for soft-water tanks with caution
3-8 dKH: Normal range for most tanks
8-15 dKH: High — African cichlids, hard water tanks
15+ dKH: Very high — rare

Important: Low KH causes pH swings. If pH varies, check KH first.

TDS (Total Dissolved Solids)

Total dissolved minerals in water. Measured in ppm.

0-5 ppm: Pure RO water — must be remineralized before use
50-150 ppm: Soft water tanks, shrimp tanks
150-300 ppm: Most freshwater tanks
300-500 ppm: Hard water tanks
500+ ppm: Very hard, limited species

Used primarily by shrimp and saltwater keepers for precise control.

Troubleshooting Common Issues

pH Suddenly Crashed

Check KH — likely too low (under 2 dKH)
Adding crushed coral or seachem KH buffer
Check water source — has it changed?

pH Won't Stay Stable

KH too low — add buffer
Tank has too much organic matter — water change
Driftwood releasing tannins acidifying water — normal for some setups

Ammonia Appearing in Established Tank

Mini-cycle from disrupted bacteria (cleaning filter media in tap water?)
Dead fish or plant decaying
Sudden overstocking
Filter failure

Nitrate Constantly High

More frequent or larger water changes
Reduce stocking
Add live plants
Reduce feeding

GH Too High in Soft Water Tank

Use RO water diluted with tap
Remove substrate that adds hardness (coral, limestone)
Add peat or driftwood (slow acidification)

Temperature Swings

Heater issue — test it
Room temperature affecting tank
Heater too small for tank size
Heater placement (away from filter intake)

Testing Frequency

For an established tank:

Daily checks: Just temperature visual (digital thermometer)
Weekly: Ammonia, nitrite, nitrate
Monthly: pH, GH, KH (for stable established tanks)
As needed: When something looks off, when adding new fish, after equipment changes

For a new/cycling tank:

Daily for first 2 weeks: Ammonia, nitrite
Every 2-3 days through cycle: Add nitrate
Weekly until stable: All standard parameters

Test Kit Recommendations

API Freshwater Master Test Kit: Standard beginner kit; covers ammonia, nitrite, nitrate, pH. ~$30.

API Saltwater Master Test Kit: Includes calcium and alkalinity for marine.

API GH/KH Test Kit: Add-on for hardness testing.

Salifert / Red Sea / Hanna instruments: Higher accuracy for serious keepers.

Avoid test strips for serious work: Convenient but less accurate. Use for quick checks only.

The Bottom Line

Six critical parameters to monitor: temperature (72-78°F most tropical), pH (6.5-7.8 typical, stable more than ideal), ammonia (always 0 ppm), nitrite (always 0 ppm), nitrate (<20-40 ppm), and GH (4-12 most species). Species-specific targets vary — softwater fish (tetras, discus) need pH 5.5-7, GH 1-8; livebearers want pH 7-8.2, GH 8-20; African cichlids need pH 7.8-8.6, GH 12-20. Stability matters more than chasing exact numbers. Test weekly for cycle parameters; monthly for hardness/pH; daily during cycling or troubleshooting. Common problems: pH crashes from low KH, nitrate buildup from overstocking, ammonia spikes from mini-cycles. Use this cheat sheet as your reference — quick lookup, no need to re-read full articles.