FRESHWATER WATER PARAMETER GUIDE (COMPLETE 2025 EDITION)

Why Water Parameters Matter in Freshwater Aquariums

Water parameters affect nearly every biological process inside your tank, including:

• Fish respiration and metabolism
• Beneficial bacteria growth
• Plant nutrient uptake
• Shell and bone formation in shrimp and snails
• Stress resistance and disease prevention

Most fish adapt to a range of conditions—but they do not tolerate sudden changes. Consistent, stable parameters matter far more than achieving “perfect numbers.”

The Most Important Freshwater Water Parameters

Here are the eight key parameters every aquarist should understand:

• Ammonia (NH₃/NH₄⁺)
• Nitrite (NO₂⁻)
• Nitrate (NO₃⁻)
• pH
• GH (General Hardness)
• KH (Carbonate Hardness)
• TDS (Total Dissolved Solids)
• Temperature

Ammonia: The Most Dangerous Parameter

Ammonia is produced from fish waste, uneaten food, and decomposing organic matter. Even small amounts burn gills and cause immediate stress.

Safe Levels

• 0 ppm only — any detectable ammonia is harmful

What Causes Ammonia Spikes?

• Overfeeding
• New tanks that haven’t cycled
• Overcleaning filter media
• Dead fish or plants hidden in the tank

How to Fix High Ammonia

• Stop feeding for 24–48 hours
• Perform a 30–50% water change
• Add live plants or bottled bacteria
• Check for decaying organic matter

Nitrite: Highly Toxic Even at Low Levels

Nitrite interferes with oxygen transport in fish blood, causing brown blood disease.

Safe Levels

• 0 ppm only

Fixing Nitrite Spikes

• Add 1–2 teaspoons of aquarium salt per 10 gallons (protects gills)
• Increase surface agitation
• Perform partial water changes
• Add beneficial bacteria boosters

Nitrate: Safe in Small Amounts

Nitrate is the final product of the nitrogen cycle. It is less toxic but still harmful in high amounts.

Recommended Nitrate Levels

• 0–20 ppm for planted tanks
• 0–40 ppm for community aquariums
• Below 10 ppm for shrimp tanks

How to Lower Nitrate

• Weekly water changes
• Add live plants
• Avoid overstocking
• Reduce feeding

pH: Acidic, Neutral, or Alkaline?

pH measures how acidic or alkaline your water is. Stability is more important than hitting a “perfect” value.

General pH Guidelines

• 6.0–7.0 — Tetras, rasboras, bettas, gouramis
• 6.8–7.6 — Most community fish
• 7.2–8.4 — Livebearers and African cichlids

What Causes pH Changes?

• Low KH (weak buffering)
• Driftwood and botanicals lowering pH
• Crushed coral or limestone raising pH
• CO₂ injection lowering pH in planted tanks

How to Keep pH Stable

• Avoid chemical “pH up/pH down” products
• Maintain adequate KH buffering
• Perform consistent water changes

GH: General Hardness (Minerals for Fish, Shrimp & Plants)

GH measures dissolved calcium and magnesium. These minerals support bones, osmotic regulation, plant health, and shrimp molting.

GH Ranges

• 1–4 dGH — Soft water (tetras, rasboras)
• 5–8 dGH — Moderate (community tanks)
• 8–12+ dGH — Hard water (livebearers, snails, cichlids)

How to Adjust GH

To raise GH:

• Crushed coral
• Wonder Shells or remineralizers
• Calcium/magnesium supplements

To lower GH:

• Mix tap water with RO/DI water

KH: Carbonate Hardness (Your pH Stability System)

KH measures carbonates and bicarbonates. These buffer your water against sudden pH swings.

KH Ranges

• 0–3 dKH: Soft, low-buffered water
• 4–8 dKH: Stable community tanks
• 8–12+ dKH: Hard-water fish

How to Raise KH

• Crushed coral
• Baking soda (very small doses)
• Kalkwasser (for advanced users)

How to Lower KH

• Mix with RO/DI water
• Use driftwood or botanicals for slow reduction

TDS: Total Dissolved Solids

TDS measures everything dissolved in your water—minerals, fertilizers, waste, salts, and more.

Recommended TDS Levels

• 100–200 ppm — Soft-water species
• 150–300 ppm — Community tanks
• 250–500 ppm — Hard-water species

How to Control TDS

• Perform weekly water changes
• Avoid overfeeding
• Use RO/DI water to dilute minerals if needed

Temperature: One of the Most Overlooked Parameters

Temperature influences metabolism, oxygen levels, and disease resistance.

Recommended Ranges

• 72–78°F — Community tanks
• 76–82°F — Bettas, gouramis, rasboras
• 74–79°F — Planted tanks
• 78–82°F — Discus
• 68–74°F — Goldfish

Temperature Tips

• Use a high-quality heater
• Avoid big swings between day and night
• Increase surface agitation in warm tanks (less oxygen)

How All These Parameters Work Together

Water chemistry is a system—changing one parameter may affect the others. For example:

• Low KH → unstable pH
• Low GH → shrimp molting failure
• High nitrates → algae blooms
• Warm water → lower oxygen levels

Your goal is to create balance, not perfection.

How to Keep Your Water Stable (Beginner-Approved Routine)

• Perform 20–30% weekly water changes
• Don’t overstock the tank
• Use live plants to absorb excess nutrients
• Test GH, KH, and pH monthly
• Test ammonia, nitrite, nitrate weekly
• Avoid chemical quick-fixes

Common Beginner Mistakes

• Using pH up/down chemicals (causes pH swings)
• Ignoring KH (leads to pH crashes)
• Replacing filter media too often
• Overfeeding (raises ammonia and nitrate)
• Mixing fish with opposite water needs

Takeaway: Stable Water = Healthy Aquariums

Freshwater aquariums don’t require perfect chemistry—they require stable chemistry. Once you understand ammonia, nitrite, nitrate, pH, GH, KH, TDS, and temperature, maintaining a thriving aquarium becomes predictable and easy. Match your fish to your natural tap water, keep a consistent maintenance routine, and prioritize stability above all else.