Aquarium Water Parameters: What Every Fishkeeper Should Know

Water is everything in fishkeeping. Your fish live in it, breathe through it, and are profoundly affected by its chemical composition every second of every day. Yet many hobbyists — especially beginners — treat water parameters as an afterthought, testing only when something goes visibly wrong. By then, damage has often already been done.

Understanding aquarium water parameters is not about chasing perfect numbers. It is about knowing what each measurement means, recognising when intervention is needed, and — just as importantly — knowing when to leave things alone. In this guide, we break down every key parameter, explain ideal ranges for common species, and provide Singapore-specific context so you know exactly what is coming out of your tap.

pH: Acidity and Alkalinity

pH measures how acidic (below 7.0) or alkaline (above 7.0) your water is, on a logarithmic scale where each whole number represents a tenfold difference. Most tropical freshwater fish thrive between pH 6.0 and 8.0, though specific preferences vary widely by species.

Ideal ranges:

• Community tropical fish: 6.5–7.5
• African cichlids: 7.5–8.5
• Discus and soft-water species: 5.5–6.8
• Caridina shrimp: 6.0–6.8
• Neocaridina shrimp: 6.5–8.0

The golden rule: stability matters far more than hitting an exact number. A steady pH of 7.6 is preferable to one that swings between 6.5 and 7.0. Only pursue active pH adjustment if your species genuinely require it and you can maintain the new level consistently. For detailed advice on lowering pH, see our pH adjustment guide.

Ammonia (NH3/NH4+)

Ammonia is the primary waste product from fish respiration, decomposing food, and dying plant matter. It exists in two forms: un-ionised ammonia (NH3), which is highly toxic, and ionised ammonium (NH4+), which is far less harmful. The proportion of toxic NH3 increases with higher pH and temperature — critically important in Singapore’s warm, sometimes slightly alkaline aquarium conditions.

Ideal level: 0 ppm. Any detectable ammonia in an established tank indicates a problem — either the biological filter has been compromised, the tank is overstocked, or something is decaying (a dead fish, uneaten food, rotting plant matter).

In a new tank undergoing the nitrogen cycle, ammonia will spike in the first one to three weeks before beneficial bacteria (Nitrosomonas) colonise the filter media and convert it to nitrite. This is normal and expected. Do not add fish until ammonia reads zero consistently.

Nitrite (NO2-)

Nitrite is the intermediate product in the nitrogen cycle. Nitrosomonas bacteria convert ammonia to nitrite, and then Nitrospira bacteria convert nitrite to nitrate. Nitrite is toxic — it binds to haemoglobin in fish blood, preventing oxygen transport (a condition called “brown blood disease”).

Ideal level: 0 ppm. Like ammonia, any detectable nitrite in an established tank signals a filtration problem. During cycling, nitrite typically peaks in weeks two to four before dropping to zero as the second group of bacteria establishes.

If nitrite spikes in an established tank, perform an immediate 50% water change and investigate the cause. Common culprits include a dead fish, a heavily cleaned filter (never rinse filter media in tap water — the chloramine in Singapore water kills beneficial bacteria), or a sudden increase in bioload.

Nitrate (NO3-)

Nitrate is the end product of the nitrogen cycle and is far less toxic than ammonia or nitrite. However, chronically high nitrate levels (above 40 ppm) stress fish, suppress immune systems, stunt growth, and fuel algae outbreaks. Very high levels (above 100 ppm) can be directly harmful, especially to sensitive species and fry.

Ideal level: Below 20 ppm for most species. Sensitive species (discus, cardinal tetras, Caridina shrimp) do best below 10 ppm. Planted tanks with fast-growing plants may show near-zero nitrate, which is fine — in these cases, you may actually need to dose nitrate as a fertiliser.

The primary way to reduce nitrate is regular water changes. For more strategies, see our article on how to reduce nitrate in your aquarium.

General Hardness (GH)

GH measures the concentration of dissolved calcium and magnesium ions. It indicates how “hard” or “soft” your water is. Hardness is measured in degrees (dGH) or ppm.

Ideal ranges:

• Soft-water species (tetras, rasboras, discus): 1–6 dGH
• Community fish: 4–12 dGH
• Livebearers (guppies, mollies): 8–20 dGH
• African cichlids: 10–25 dGH
• Caridina shrimp: 4–6 dGH
• Neocaridina shrimp: 6–12 dGH

GH is particularly important for shrimp. Calcium and magnesium are essential for building new shells after moulting. Too-low GH causes moulting failures; too-high GH makes the old shell too rigid to shed. For shrimp keepers, GH is arguably more important than pH.

Carbonate Hardness (KH)

KH measures the concentration of carbonate and bicarbonate ions — the water’s “buffering capacity.” Higher KH resists pH changes; lower KH allows pH to fluctuate. Think of KH as a seatbelt for your pH: the higher it is, the more stable your pH, but the harder it is to adjust intentionally.

Ideal ranges:

• Planted tanks with CO2: 2–5 dKH (allows pH to drop with CO2 injection)
• Community tanks without CO2: 3–8 dKH (provides stability)
• African cichlid tanks: 8–15 dKH
• Caridina shrimp (with active substrate): 0–2 dKH

A KH below 1 dKH is risky because there is no buffer against pH crashes. If your tank runs very low KH (common with active substrates and RO water), monitor pH frequently and consider adding a small amount of crushed coral to provide a minimal buffer.

Total Dissolved Solids (TDS)

TDS measures everything dissolved in your water — minerals, salts, metals, organic compounds — in ppm. It is a general indicator rather than a specific measurement. TDS increases over time as water evaporates (concentrating dissolved substances) and as fertilisers, food, and waste add to the total.

Typical ranges:

• Caridina shrimp: 100–150 ppm
• Neocaridina shrimp: 150–250 ppm
• General freshwater: 150–400 ppm

TDS is most useful for shrimp keepers who remineralise RO water — you can use a TDS meter to dose remineraliser to a precise target. For general fishkeeping, TDS is less actionable than specific measurements like GH, KH, and nitrate.

A TDS pen costs S$10–20 and gives instant readings. Just remember that TDS tells you how much is dissolved, not what — a high TDS reading could mean high minerals (harmless) or high nitrate and waste (harmful). Pair TDS monitoring with regular liquid testing for a complete picture.

Temperature

Most tropical freshwater fish thrive between 24 and 28 degrees Celsius. In Singapore, ambient room temperature keeps aquarium water at 27–31 degrees without a heater, which suits most tropical species. In air-conditioned rooms, water may drop to 24–25 degrees during the night — generally still acceptable but worth monitoring for sensitive species.

Key considerations:

• Avoid temperature swings of more than 2 degrees Celsius within a single day. Air conditioning cycling on and off is a common cause.
• During water changes, match the replacement water temperature to the tank. Cold tap water dumped into a warm tank can trigger ich outbreaks.
• Higher temperatures (above 30 degrees) reduce dissolved oxygen and accelerate fish metabolism, meaning more waste production. If your tank runs consistently above 30 degrees, consider a fan-based cooling system or aquarium chiller.
• Certain species — notably Crystal Red shrimp and some cold-water Hillstream loaches — require temperatures below 26 degrees, which necessitates a chiller in Singapore’s climate.

Testing Methods: Liquid vs Strip

For serious fishkeeping, a liquid test kit is essential. The API Freshwater Master Test Kit (testing pH, high-range pH, ammonia, nitrite, and nitrate) is the most popular choice in Singapore and provides hundreds of tests per kit. Supplement with separate GH and KH test kits if you keep shrimp or soft-water species.

Singapore Tap Water Parameters

Singapore’s PUB-treated tap water is generally consistent, but parameters can vary slightly depending on the source (local reservoir, imported water, NEWater, or desalinated water). Here are the typical baseline values:

Singapore tap water is relatively soft with low to moderate buffering capacity. This is advantageous for keeping soft-water species with minor adjustments, but means the pH can shift relatively easily if KH is not monitored. Always treat tap water with a conditioner that neutralises chloramine (not just chlorine) — Seachem Prime is the most popular choice locally.

Test your own tap water every few months, as parameters can shift seasonally or when PUB adjusts its source blend.

When to Adjust vs Leave Alone

One of the most common mistakes in fishkeeping is constantly chasing “perfect” parameters. Here is a simple framework:

Adjust when:

• Ammonia or nitrite is above zero in an established tank — do an immediate water change.
• Nitrate exceeds 40 ppm — increase water change frequency or volume.
• You keep species with specific, non-negotiable requirements (Caridina shrimp, discus) and your water is significantly outside their range.
• pH is outside the 6.0–8.0 range for standard tropical fish.

Leave alone when:

• Your pH is 7.4 and your tetras are healthy, active, and showing good colour — even though “ideal” says 6.5. Acclimated fish tolerate a wide range as long as it is stable.
• GH is slightly outside the textbook range but your fish are thriving. Many species are more adaptable than care sheets suggest, especially captive-bred specimens.
• TDS is higher than a guide suggests, but ammonia, nitrite, and nitrate are all in check. TDS alone is not a reason to act.

The single most important thing is consistency. Chasing numbers with constant adjustments creates more instability — and more stress — than a slightly imperfect but rock-steady reading.

Water Change Schedule Based on Parameters

Always match replacement water temperature and treat with a dechlorinator before adding to the tank. In high-tech planted tanks, some aquascapers pre-mix replacement water with fertilisers to maintain consistent nutrient levels after the change.

Frequently Asked Questions

How often should I test my water?

In a stable, established tank: once a week, ideally on the same day as your water change (test before the change). During cycling, after adding new fish, or if anything seems off: test daily. Keeping a log — even a simple one on your phone — helps you spot trends before they become problems.

My test kit shows a slightly yellow-green colour for nitrate. Is that 10 or 20 ppm?

The API nitrate test is notoriously difficult to read between 10 and 20 ppm. Shake bottle #2 vigorously for at least 30 seconds and bang it against a hard surface to ensure the reagent is properly mixed — it settles and gives false low readings if not shaken thoroughly. If in doubt, treat it as 20 ppm and maintain your water change schedule.

Do I need a TDS meter?

If you keep Caridina shrimp and remineralise RO water, a TDS meter is essential. For general fishkeeping, it is a nice-to-have but not necessary — your liquid test kits provide more actionable information. TDS meters are cheap (S$10–20) and give instant readings, so there is no harm in having one.

Can I use bottled mineral water instead of tap water?

Technically yes, but it is impractical and expensive for regular water changes. More importantly, the mineral content varies between brands and batches, making consistency difficult. Singapore’s tap water is clean, low in contaminants, and well-suited for aquarium use with a quality dechlorinator. Save the bottled water for drinking.

Understanding your water is the foundation of successful fishkeeping. If you would like professional help setting up a monitoring routine or troubleshooting water quality issues, contact the Gensou team. Our maintenance service includes comprehensive water testing and parameter management as part of every visit.

Related Reading

• Aquarium Cloudy After Water Change: Why and How to Fix It
• How Often to Change Aquarium Water: Finding Your Schedule
• Water Change Temperature Matching: Why It Matters
• Aquarium Water Conditioners Explained: Prime, Safe and Beyond
• Best Water Conditioners for Aquariums: Singapore Tap Water Guide