Most fish problems are water problems. Once you understand that, the hobby gets a lot easier.

New hobbyists tend to focus on the visible stuff: which fish look good together, what decorations to use, which filter to buy. Water chemistry is often overlooked and a little intimidating. But here's the reality: a fish can survive in a plain tank with basic decorations and a cheap filter. It cannot survive in water with elevated ammonia, wildly swinging pH, or the wrong temperature.

Water quality is not advanced knowledge. It's the foundation. Learn the basics once and you'll have them for the life of your tank.

This guide explains every parameter you need to know, what each one does, what the target ranges are, how to test correctly, and what to do when something is off.

The Parameters You Actually Need to Monitor

There are six core parameters for a freshwater tank. You don't need to understand the deep chemistry behind each one. You just need to know what it measures, why it matters, and what number you're aiming for.

1. Ammonia (NH3)

What it is: The first and most toxic waste product in any aquarium. Fish produce ammonia constantly through their waste and respiration. Uneaten food and decaying plant matter also break down into ammonia.

Why it matters: Even small amounts of ammonia can damage fish gills and suppress their ability to absorb oxygen. At higher concentrations it is rapidly lethal. In a new, uncycled tank, ammonia has nowhere to go and builds up fast. In a cycled tank, beneficial bacteria convert it before it accumulates.

Target: 0 ppm at all times. There is no safe level above zero.

What causes it to spike: New tank with no bacteria colony, overstocking, overfeeding, a dead fish going unnoticed, filter failure, or a large water change that disrupts the bacterial colony.

What to do if it's elevated: Do a 25-30% water change immediately to dilute it. Find and remove the source. Do not add fish until it returns to zero.

2. Nitrite (NO2)

What it is: The second stage of the nitrogen cycle. Beneficial bacteria convert ammonia into nitrite. Nitrite is still toxic, just somewhat less so than ammonia.

Why it matters: Nitrite interferes with the ability of fish blood cells to carry oxygen. High nitrite causes a condition sometimes called "brown blood disease" where fish essentially suffocate despite normal oxygen levels in the water. You'll see fish gasping, lethargic, and pale.

Target: 0 ppm. Like ammonia, there is no safe reading above zero.

What causes it to spike: The same events that cause ammonia spikes, typically in the following days as the ammonia converts. Also seen after filter media is replaced, the tank is medicated with antibacterial treatments, or the cycle is disrupted.

What to do if it's elevated: Partial water change to dilute, identify and fix the cause.

3. Nitrate (NO3)

What it is: The end product of the nitrogen cycle. A second group of bacteria converts nitrite into nitrate. Nitrate is far less toxic than ammonia or nitrite and accumulates gradually over time.

Why it matters: At low to moderate levels, nitrate is tolerable for most fish. At high levels (above 40-80 ppm depending on species), it causes chronic stress, suppresses the immune system, makes fish more susceptible to disease, and stunts growth over time. Shrimp and sensitive species like discus feel the effects at much lower concentrations.

Target: Below 20 ppm for sensitive fish and shrimp. Below 40 ppm for most community fish. The lower the better.

What causes it to rise: Nitrate accumulates naturally in all aquariums. Overfeeding, overstocking, and infrequent water changes all accelerate the buildup.

What keeps it in check: Regular partial water changes (the primary method), live plants (which consume nitrate as fertiliser), and not overfeeding.

4. pH

What it is: A measure of how acidic or alkaline the water is, on a scale from 0 to 14. A pH of 7.0 is neutral. Below 7.0 is acidic. Above 7.0 is alkaline.

Why it matters: Different fish originate from different environments. Tetras and bettas come from soft, acidic South American or Southeast Asian waterways. African cichlids come from hard, alkaline rift lakes. Keeping fish in water outside their preferred pH range causes ongoing stress. Importantly, the toxicity of ammonia also increases significantly at higher pH levels, so a tank with pH 8.0 and a small ammonia reading is more dangerous than the same ammonia reading at pH 6.5.

Target range: Most community freshwater fish are comfortable between pH 6.5 and 7.8. Check the requirements of the specific species you're keeping.

Australian note: Tap water pH varies significantly around Australia. Sydney and Melbourne water tends to sit between 7.0 and 7.8. Brisbane water is often closer to 7.5-8.0, while Adelide and in particular Perth can be closer to pH 8.0. Regional and rural water varies more widely. It's worth knowing your local starting point, as it determines which fish suit your tap water naturally.

What to do if pH is wrong: The most important rule is consistency. A stable pH that's slightly outside the ideal range is far less harmful than a pH that swings by a full point between water changes. If you need to adjust pH, do it slowly over days, never all at once.

To raise pH: crushed coral or limestone in the filter, or commercial pH-up products. To lower pH: driftwood, Indian almond leaves, or peat in the filter media all naturally acidify water gradually.

5. General Hardness (GH)

What it is: A measure of dissolved minerals in the water, primarily calcium and magnesium. Expressed in dGH or ppm. Hard water has high mineral content. Soft water has low mineral content. GH is often the least checked, but most important water quality parameter to meet for happy/heathy fish.

Why it matters: Fish and invertebrates use calcium and magnesium for a range of biological functions. Shrimp and snails need calcium to build and maintain their shells. Fish osmoregulate (manage their internal salt and water balance for survival) differently in hard versus soft water. Keeping a fish adapted to soft water in very hard water, or vice versa, causes long-term stress even if other parameters look fine.

Target: 4-12 dGH (70-200ppm) covers most common community fish. Shrimp-specific requirements vary more and are covered in our shrimp guide.

Australian note: Water hardness varies enormously by location in Australia. Melbourne's water is notably soft (often GH 1-3 dGH), which is excellent for tetras, bettas, and soft-water plants but needs mineral supplementation for shrimp. Perth's water is much harder. Knowing your local GH saves you from chasing problems that are simply a mismatch between your water and your livestock.

6. Carbonate Hardness (KH)

What it is: A measure of the water's ability to buffer (protect) against changes in the water pH, specifically it measures how much carbonate and bicarbonate is dissolved in it. Also called alkalinity.

Why it matters: KH is your pH's safety net. It resists sudden pH swings. A tank with high KH holds a stable pH even as the natural processes of the nitrogen cycle (which produce nitric acid and push pH down over time) work away at it. A tank with very low KH is vulnerable to sudden pH crashes, which can stress or kill fish rapidly.

Target: 3-8 dKH (50-140 ppm)for most freshwater community tanks.

What to do if KH is low: Add crushed coral to the filter, use a commercial KH buffer, or do more frequent small water changes with harder tap water. Avoid large water changes with very soft or RO water in a low-KH tank as it dilutes the buffering ability further.

7. Temperature

What it is: Not a chemical parameter per se, but arguably the most important single factor in fish health. Fish are cold-blooded. Their metabolism, immune function, digestion, and behaviour are all directly controlled by water temperature.

Why it matters: A fish kept 3-4°C below its preferred temperature will eat poorly, move slowly, have a suppressed immune system, and be more susceptible to disease. A fish kept above its preferred temperature will be oxygen-deprived, hyperactive, and similarly prone to illness. Sudden temperature swings, such as a heater failure overnight in winter, are one of the most common causes of sudden fish death.

Target: Varies by species. Most tropical community fish: 24-27°C. Bettas: 25-27°C. Goldfish and native species: often comfortable at 18-22°C without a heater.

Australian note: In summer, unheated tanks in warm rooms in Queensland or Western Australia can climb to 30°C or above. Warm water holds less dissolved oxygen and accelerates bacterial growth including harmful pathogens. Keep an eye on temperature during heatwaves, not just in winter.

Tap Water in Australia: What You're Starting With

Before you can manage your water parameters, you need to know what comes out of your tap. Australian tap water varies considerably by location and has a few specific characteristics worth understanding.

Chlorine and chloramine: All Australian municipal water supplies add either chlorine or chloramine, but often both, to make the water safe to drink. Both are toxic to fish and to the beneficial bacteria in your filter. Always treat tap water with a dechlorinator before it enters the tank.

Standard chlorine evaporates if you leave water in a bucket for 24 hours. Chloramine does not. Many Australian councils use chloramine (often in summer) rather than standard chlorine. A quality dechlorinator rated for chloramine removes both instantly and is the safer choice regardless of which your water provider uses.

pH: Most Australian capital city tap water is slightly alkaline, typically sitting between 7.0 and 8.0. It's treated to prevent pipe corrosion, which often raises pH slightly above neutral.

Hardness: This is where Australia varies the most. Melbourne's soft, slightly acidic water from catchment reservoirs is very different to the harder, more alkaline water found in many other parts of the country. If you're setting up a tank and want to understand your local starting point, your water provider's annual water quality report is publicly available online and lists pH, hardness, and other parameters.

The practical takeaway: For most community fish, Australian tap water treated with a dechlorinator is perfectly fine as a base. The water chemistry may favour certain species over others, but rather than fighting your tap water, it's often smarter to choose fish that suit what you already have.

How to Test Your Water Properly

Liquid test kits vs test strips

There are two main options for home testing: liquid test kits and dip strips.

Liquid test kits (the Aquasonic test kit or API Freshwater Master Test Kit are the standard recommendations) use chemical reagents added to a water sample. They're more time-consuming but significantly more accurate. The Aquasonic or API kit covers ammonia, nitrite, nitrate, and pH, and includes over 800 tests. These kits should be used when troubleshooting a problem or cycling a new tank.

Test strips dip into the tank and change colour within seconds. They're fast and convenient for routine checks. The drawback is accuracy: they can be unreliable at low concentrations where precision matters most, and they don't test for ammonia. However, they are a great option for a rapid and quick general assessment and are often used for regular monitoring. Use a liquid kit when something seems wrong.

How often to test

New tank (cycling phase): Every 2-3 days minimum. You need to track ammonia, nitrite, and nitrate rising and falling to confirm the cycle is running.

Established tank, regular maintenance: Once a week is sufficient for ammonia, nitrite, and nitrate. Temperature should be checked every few days, especially in seasonal transition periods. pH and hardness can be tested monthly once you know your baseline is stable.

When something is wrong: Test immediately and test everything. Don't guess.

How to read results accurately

Compare your test vial colours in natural light, not under tank lighting or yellow indoor lighting, which can shift the apparent colour. Hold the vial against the white card provided in the kit and compare at eye level.

Write results down. A simple notebook or notes app with the date and readings creates a log that tells you whether parameters are stable or drifting over time. This is far more useful than a single test result taken in isolation.

The Weekly Maintenance Routine

Good water quality is mostly maintained through consistent, simple weekly habits rather than constant interventions.

Weekly water change: Replace 20-25% of the tank volume with fresh, dechlorinated water matched to the tank temperature. This is the single most effective water quality maintenance action you can take. It removes accumulated nitrates, replenishes minerals, and dilutes any compounds that have been slowly building.

Gravel vacuum: Use a siphon vacuum during water changes to remove waste from the substrate. Decomposing waste buried in gravel is a continuous source of ammonia and nitrate. You don't need to vacuum every centimetre every week. Work through a third of the tank each time.

Check the filter: Make sure it's running and flow hasn't dropped. A clogged filter is a failing biological filter. Every 4-6 weeks, rinse the filter media in a bucket of old tank water (never tap water, which would kill the bacteria due to the chlorine and chloramines) to remove sludge buildup.

Check the temperature: Heaters fail. Thermometers drift. A quick check takes five seconds.

When Parameters Go Wrong: Quick Fixes

The One Rule That Matters More Than Any Number

Stability beats perfection.

A tank with pH 7.8 that has been stable at 7.8 for three months is a healthy environment. A tank that swings between 7.0 and 8.0 every week is a stressful one, even though both readings individually look fine on paper.

Fish adapt to consistent conditions. What they cannot adapt to is constant change. If your tap water produces a slightly alkaline, moderately hard tank that holds stable, your fish will thrive in it. Choose livestock that suits your water rather than constantly fighting your chemistry, and focus on keeping things consistent rather than chasing ideal numbers.

That mindset, combined with weekly water changes and a liquid test kit used regularly, covers 90% of what water quality management actually requires.

If you have questions about your local water conditions or need help choosing the right test kit or water conditioner for your setup, get in touch with the team at LiveFish. We're happy to help you get the foundation right before the fish go in.