Water Parameters & Chemistry: The Invisible Keys to Success

Water chemistry is invisible to the naked eye but critical to fish health. Understanding and managing these parameters separates thriving aquariums from struggling ones.

The Essential Parameters

1. pH (Acidity/Alkalinity)

What it measures: How acidic or alkaline your water is
Scale: 0-14 (7 is neutral)
Most tropical fish: 6.5-7.5
Goldfish: 7.0-8.4
African Cichlids: 7.8-8.6

Why it matters:

Affects fish metabolism and stress levels
Influences toxicity of ammonia (more toxic at higher pH)
Impacts bacterial function in filter
Affects fish ability to maintain internal salt balance

How to test:

Best: API pH Test Kit (liquid, $8)
Alternative: Digital pH meter ($15-50, needs calibration)
Avoid: Test strips (not accurate enough)

Adjusting pH:

To Lower pH (Make More Acidic):

Add driftwood (releases tannins)
Add peat moss to filter
Indian Almond Leaves (Catappa)
RO water (removes carbonates)
Chemical: pH Down products (use sparingly)

To Raise pH (Make More Alkaline):

Add crushed coral or aragonite to filter
Add limestone or marble decorations
Baking soda (1 tsp per 5 gallons, carefully)
Chemical: pH Up products

⚠️ WARNING: Sudden pH changes are more dangerous than “imperfect” pH. Change pH by no more than 0.2 per day.

2. Ammonia (NH3/NH4+)

Target: 0 ppm always
Dangerous: >0.25 ppm
Lethal: >1-2 ppm

Ammonia is the most toxic compound in aquariums. It burns fish gills, skin, and internal organs.

Sources:

Fish waste (primary source)
Decaying food and plants
Decomposing fish
Chloramine in tap water

Testing:

Essential: API Ammonia Test Kit
Digital: Hanna Ammonia Checker
Frequency: Daily during cycling, weekly thereafter

Emergency Treatment:

Water change (50% immediately)
Add Seachem Prime (detoxifies for 24-48 hours)
Check filter function
Reduce feeding by 50%
Test daily until resolved

3. Nitrite (NO2-)

Target: 0 ppm always
Dangerous: >0.5 ppm
Lethal: >1-2 ppm

Nitrite prevents blood from carrying oxygen. Fish suffocate internally even with plenty of oxygen in the water.

Symptoms of nitrite poisoning:

Rapid breathing/gasping
Brown or tan gills
Lethargy
Fish gathering at surface

Emergency Treatment:

Large water change (50-75%)
Add aquarium salt (1 tsp per 10 gallons)
Increase aeration
Test and change water daily until 0 ppm

4. Nitrate (NO3-)

Target: <20 ppm for sensitive fish
Acceptable: <40 ppm
Too high: >80 ppm

While less toxic than ammonia/nitrite, high nitrates stress fish and promote algae.

Control methods:

Weekly 25-50% water changes
Live plants (consume nitrates)
Don’t overfeed
Proper stocking levels

5. General Hardness (GH)

What it measures: Total dissolved minerals (calcium, magnesium)
Scale: Degrees German (dGH) or ppm
Soft water: 0-4 dGH (0-70 ppm)
Moderately hard: 4-12 dGH (70-210 ppm)
Hard water: 12-30 dGH (210-530 ppm)

Why it matters:

Affects fish osmoregulation (fluid balance)
Discus, tetras, rasboras prefer soft water
African cichlids, livebearers prefer hard water
Snails and shrimp need calcium (hardness)

Fish by Hardness Preference:

Soft Water (0-6 dGH):

Discus
Cardinal Tetras
Neon Tetras
Angelfish
Rasboras
Corydoras (most species)
Bettas

Moderate Water (6-12 dGH):

Most community fish
Guppies
Platies
Mollies
Danios

Hard Water (12-20+ dGH):

Goldfish
African Cichlids
Livebearers
Rainbowfish

Adjusting Hardness:

To Lower (Softer):

Mix with RO or distilled water
Use peat moss
Add driftwood

To Raise (Harder):

Crushed coral or aragonite
Limestone decorations
Wonder Shells (calcium blocks)
Cuttlebone (for snails/shrimp)

6. Carbonate Hardness (KH/Alkalinity)

What it measures: Water’s buffering capacity (ability to resist pH changes)
Target: 4-8 dKH (70-140 ppm)
Too low: <3 dKH (pH will swing wildly)
Too high: >12 dKH (hard to adjust pH)

Why it’s critical:

Stabilizes pH (prevents crashes)
Provides carbon for plants
Affects bacterial function

How to increase KH:

Baking soda (carefully, 1 tsp per 10 gallons)
Crushed coral in filter
Commercial KH buffers

How to decrease KH:

Mix with RO water
Peat moss
Note: Hard to lower - better to adapt fish to your water

The Relationship Between Parameters

pH and Ammonia Toxicity

At higher pH, ammonia becomes MORE toxic:

pH 6.0: Ammonia is mostly harmless ammonium (NH4+)
pH 7.0: 50% ammonia (toxic), 50% ammonium
pH 8.0: 90%+ is toxic ammonia (NH3)

Implication: High pH tanks are less forgiving of ammonia spikes.

GH and KH Relationship

GH = calcium + magnesium (total hardness)
KH = carbonate + bicarbonate (buffering capacity)
They often correlate but not always
You can have hard water with low KH (pH will drift)
You can have soft water with high KH (rare but possible)

Testing Schedule by Tank Type

New Tank (Cycling):

Daily: Ammonia, Nitrite
Every 2-3 days: Nitrate, pH
Weekly: GH, KH

Established Community Tank:

Weekly: Ammonia, Nitrite, Nitrate, pH
Monthly: GH, KH

High-Tech Planted Tank:

Weekly: Full panel plus CO2, phosphate, iron

Sensitive Species (Discus, Shrimp):

Every 2-3 days: Full panel

Water Parameter Quick Reference

Parameter	Freshwater Tropical	Goldfish	Discus	African Cichlids	Shrimp
pH	6.5-7.5	7.0-8.4	6.0-7.0	7.8-8.6	6.5-8.0
Ammonia	0 ppm	0 ppm	0 ppm	0 ppm	0 ppm
Nitrite	0 ppm	0 ppm	0 ppm	0 ppm	0 ppm
Nitrate	<40 ppm	<40 ppm	<20 ppm	<40 ppm	<20 ppm
GH	3-12 dGH	8-20 dGH	1-4 dGH	12-20 dGH	6-12 dGH
KH	4-8 dKH	6-12 dKH	2-4 dKH	8-16 dKH	4-8 dKH
Temperature	75-80°F	65-72°F	82-86°F	75-80°F	72-78°F

When to Test & What to Do

Daily Testing Scenarios:

New tank cycling
Fish showing signs of illness
After adding new fish
After equipment failure
After using medications

Weekly Testing:

Established tanks during maintenance
Before water changes
When planning to add fish

Monthly Testing:

General parameter trends
GH/KH (stable parameters)
TDS (Total Dissolved Solids) if you have a meter

Common Water Chemistry Mistakes

Testing with expired kits - Replace liquid tests annually
Not testing tap water - Know your baseline
Chasing “perfect” pH - Stability is better than ideal numbers
Using pH chemicals - They create swings; use natural methods
Ignoring KH - Leads to pH crashes
Testing at wrong time - Test before water changes, not after
Not writing down results - Trends matter more than single readings

2026 Advanced Testing Options

Electronic Meters

Multi-Parameter Probes:

Measure pH, temperature, conductivity
Examples: Hanna Combo Pen ($50-80)
Requires calibration

TDS Meters:

Measure total dissolved solids
Good for monitoring RO water and water change efficiency
Cheap ($10-20)

Continuous Monitors

Seneye:

Continuous ammonia, pH, temperature monitoring
$200+ but invaluable for sensitive tanks
Connects to smartphone app

Smartphone-Connected Testers

New in 2026:

Devices that use phone cameras to read test colors
More accurate than eyeballing
Examples: Various apps and attachments ($20-40)

Conclusion

Water chemistry isn’t just about hitting specific numbers—it’s about maintaining stability. Fish adapt to a wide range of parameters, but they cannot handle rapid changes.

Golden Rules:

Test regularly
Make gradual changes
Match water parameters when adding new fish
Keep records to spot trends
When in doubt, do a water change

Remember: Expensive fish and equipment mean nothing if water chemistry is neglected. Master your water, and you’ve mastered 80% of aquarium keeping.

Last Updated: January 2026
Next Review: July 2026