Water Quality

Betta Gillfriend care rules: one betta per tank. Mirror or flare practice: one 2-minute session a day, with at least 2 rest days a week. Train: up to 10 minutes a week.

Merck Veterinary Manual puts it plainly: poor water quality is the most common cause of environmental disease in fish. Most betta illnesses start with, or are made worse by, water problems. The good news is that water quality is something you can measure and control.

Target parameters

Parameter	Target for bettas	Why it matters	Notes
Temperature	76–81°F (about 24–27°C), steady	Bettas are tropical; swings weaken immunity	Use a heater and thermometer. Change it no faster than about 1°C per hour.
Ammonia (total, TAN)	0 ppm	Burns gills and skin; can be lethal	RSPCA Australia: under 0.1 ppm. A research colony notes harm above 0.25 ppm. More toxic at higher pH and temperature.
Nitrite (NO₂⁻)	0 ppm	Causes "brown blood disease"; blood can't carry oxygen	RSPCA Australia: under 0.2 ppm. Merck's reference value is 0. Chloride (salt) in the water helps protect fish against nitrite.
Nitrate (NO₃⁻)	Under 20 ppm ideally; never above 50 ppm	Long-term stress at high levels	Merck's freshwater reference: under 20 mg/L. RSPCA Australia: under 50 ppm.
pH	About 6.5–7.5, stable	Affects ammonia toxicity and the biofilter	PetMD says bettas tolerate about 6.5–7.8, and a pH close to your tap water makes water changes safer.
General hardness (GH)	Not too soft: above about 20 mg/L (1 dGH)	Fish absorb minerals from water	Merck's freshwater reference range: above 20 mg/L. Don't use distilled water alone.
Carbonate hardness / alkalinity (KH)	Enough to keep pH stable	Buffers pH; feeds the biofilter	Merck's freshwater reference range: above 100 mg/L. Low alkalinity lets pH crash.
Chlorine and chloramine	0	Highly toxic even at tiny amounts	Always use a water conditioner on tap water.
Dissolved oxygen	Above 5 mg/L	Even air-breathers need oxygenated water for their gills	Gentle surface movement helps.

Tip: Many test kits report nitrite and nitrate "as nitrogen" (NO₂-N and NO₃-N). Merck notes you multiply NO₂-N by 3.3, and NO₃-N by 4.4, to get the actual nitrite or nitrate. Check your kit's instructions so you're comparing the right numbers.

Why ammonia gets worse at high pH

Test kits usually measure total ammonia, which is a mix of toxic ammonia (NH₃) and much less toxic ammonium (NH₄⁺). The higher the pH (and, less so, the temperature), the more of it is in the toxic form. Merck notes that a calculated NH₃ level of 0.05 mg/L is enough to damage gill tissue. For a pet keeper the simple rule is: any detectable ammonia is a problem to fix.

Warning: If ammonia is very high and the pH is low (acidic), a big sudden water change that raises pH can turn harmless ammonium into toxic ammonia all at once. Match the new water's pH and temperature to the tank as closely as you can, consider an ammonia-binding conditioner, and if you're unsure, ask an aquatic vet.

Testing

Use a liquid test kit for ammonia, nitrite, nitrate and pH. Liquid kits are generally more precise than dip strips, and owning one means you can test the moment something looks wrong.
New tank (first 6 weeks): RSPCA Australia suggests testing ammonia and nitrite every 2–3 days.
Established tank: test weekly (PetMD), or every 1–2 weeks (RSPCA).
Always test when: your betta looks unwell, after adding anything new, after medicating, if the water looks cloudy or smells, or after a power cut.
Test your tap water too, once, so you know what you're starting with. Some tap water contains ammonia or chloramine, and the Illinois vet hospital recommends checking for heavy metals.

Tip: Log your results in the app. Trends ("nitrate creeps up faster than it used to") tell you more than a single reading.

Water changes

Tank situation	Suggested routine
Established, cycled tank	10–25% weekly (RSPCA Australia), or 15–25% weekly (PetMD), with a gentle gravel vacuum
Smaller tank or heavier feeding (giants)	Lean towards the higher end, or two smaller changes a week
New, uncycled tank with a fish	Test daily; change water whenever ammonia or nitrite is detectable
Emergency (ammonia or nitrite spike)	Large change: Merck recommends 50% or more when ammonia is high, taking care with pH (see the warning above)

How to do a water change

Unplug the heater (and filter if needed) for safety, following the equipment instructions.
Siphon water into a dedicated fish-only bucket, vacuuming waste from the substrate. Never suck on the hose to start a siphon (RSPCA).
Prepare new water: treat it with water conditioner and match the temperature to the tank with a thermometer.
Pour new water in gently, onto a plate, decoration or your hand, so you don't blast your betta or the substrate.
Plug equipment back in and check the temperature again after a few minutes.

Warning: "Topping up" evaporated water is not a water change. Merck describes old tank syndrome: when old water is never removed, acids build up, buffering is used up, pH crashes, the biofilter dies, and ammonia spikes. Always remove old water and replace it.

Tip: Clean filter media in removed tank water, not tap water, and only when it's clogging or about monthly (RSPCA). Don't scrub everything at once. The good bacteria live on surfaces.

Dechlorinator (water conditioner)

Tap water is treated with chlorine or chloramine to make it safe for people. Both are highly toxic to fish. Merck notes harm at chlorine levels as low as 0.02 mg/L.
Use a conditioner that treats both chlorine and chloramine, every time you add tap water, dosed for the volume of new water you're adding (or the whole tank, per the label).
Chloramine contains ammonia. When a conditioner breaks chloramine apart, ammonia can be released. A conditioner that also binds ammonia is a sensible choice, especially in newer tanks.
Measure your tank and bucket volumes accurately so you dose correctly.
Do not use distilled or pure RO water on its own. It lacks the minerals fish need (Illinois vet hospital; Merck).

Warning: Never use soap, detergent or household cleaners on anything that goes in the tank, including buckets, sponges and decorations (RSPCA).

Acclimation: bringing a betta home

The goal is to avoid sudden changes in temperature and water chemistry, and to avoid bringing in disease.

Ideally, acclimate into a quarantine tank, not your main tank (see Choosing and buying).
Keep the trip short and dark. Keep the bag or cup out of direct sun and cold.
Match temperature slowly. Float the sealed bag or cup in the tank so the temperatures meet. Many keepers float for about 15–30 minutes. Merck's general guideline is that temperature shouldn't change faster than about 1°C (or 1°F) per hour, so if the shop water is very different, go slower.
Mix water gradually. Add small amounts of tank water to the bag every few minutes over a period of time, so your betta adjusts to the new pH and hardness.
Net the fish across. Gently move your betta into the tank with a soft net or a cup, and throw the store water away rather than pouring it into your tank, as it can carry waste and pathogens.
Lights low, no food on day one. Let your betta settle. Offer a small meal the next day.

Tip: Stress stripes, pale colour and hiding are common on day one. Most bettas colour up and start exploring within a few days. If not, check your water and see Behaviour and body language.

Know your tap water (Canada edition)

Your tap water is the starting point for everything in the tank, so it's worth a little detective work.

Look up your city's water quality report. Most Canadian municipalities publish yearly reports listing pH, hardness and the disinfectant they use. Search "[your city] drinking water quality report".
Chlorine or chloramine? Both kill filter bacteria and harm gills. Chloramine doesn't gas off if you leave water standing, so always use a dechlorinator that says it handles both.
Hardness: water in much of the Prairies and Southern Ontario tends to be hard, while coastal BC, the Canadian Shield (much of northern Ontario and Québec) and parts of the Atlantic provinces tend to have soft water. Check your local report; it varies a lot even within a province. Bettas adapt to a wide range if it's stable. Chasing a "perfect" pH with chemicals usually causes more harm than good.
Hot water tap: use cold water and warm it, or mix carefully. Hot water tanks can add metals and sediment.
Home water softeners swap calcium and magnesium for sodium. Use a tap that bypasses the softener.
Well water: test for ammonia, nitrate, pH, hardness and metals (copper, iron) before using it. Some wells have high nitrate from farmland.
Distilled or reverse-osmosis (RO) water has almost no minerals. Don't use it alone; it needs remineralising to safe GH and KH levels.

Tip: Test your tap water once for ammonia, nitrate and pH, and write the numbers down. If your tank ever shows "mystery ammonia", you'll know if it came from the tap.

GH and KH in plain language

GH (general hardness) is how much calcium and magnesium is dissolved in the water. Fish and plants use these minerals. 1 dGH = about 17.9 mg/L (ppm).
KH (carbonate hardness, or alkalinity) is the water's pH buffer. Low KH lets pH drop suddenly, sometimes called a "pH crash", especially in older, uncleaned tanks, because the biofilter produces acid as it works. 1 dKH = about 17.9 mg/L as CaCO₃.
For bettas: stable is more important than exact. Avoid very soft, unbuffered water (KH near zero) unless you know how to manage it, and avoid big jumps during water changes.

Sources

Care guide by Betta Gillfriend (Bespok Labs, BC, Canada). It is general information, not vet advice. If your betta is sick, ask an aquatic vet.