Other Aspects of Fish Tank Water Management

Most people land on a page like this after a familiar moment: the tank looks fine, then the water clouds, algae creeps in, or a fish starts acting “off” — and you need to work out what to test, what to adjust, and what to leave alone.

In a closed box of water, small changes travel fast. Temperature swings can stress fish. A disrupted biofilter can turn ordinary waste into toxic ammonia. This guide keeps things practical: what matters most, what “normal” looks like, and the steady routine that keeps an aquarium stable.

Start with stability: temperature, oxygen, and flow

Fish cope far better with steady conditions than perfect numbers that swing around. Temperature is a quiet driver in the background: it affects fish metabolism, dissolved oxygen, and how quickly waste breaks down.

Use a heater sized for your aquarium (tropical tanks) and a thermometer you actually check. Place the filter outlet so it ripples the surface; surface movement helps oxygen exchange, and oxygen is essential for both fish and the bacteria living in your filter media.^{1, 2}

Quick temperature checks

• Check daily when seasons change or the room is heated/cooled.
• Avoid big swings. Sudden changes are often more stressful than a slightly “wrong” but stable temperature.²
• Don’t trust tiny bowls to hold temperature steady; they fluctuate too easily and are hard to filter well.³

Water chemistry: what to measure (and what not to obsess over)

Water chemistry is not a single “ideal range” for every aquarium. pH and hardness should suit the species you keep, but stability matters more than chasing a universal target with constant additives.

A common mistake is treating pH as the main problem, when the real issue is usually waste management (ammonia/nitrite), overfeeding, or a filter that’s been cleaned too aggressively.

What to test routinely

• Ammonia and nitrite (especially in new tanks, after filter problems, or after adding fish).
• Nitrate (to track waste build-up over time and guide water-change frequency).
• pH (mainly to catch sudden shifts, and to match species needs).

The nitrogen cycle: the engine room of water quality

Fish constantly release waste. Left alone, that waste becomes ammonia, which can harm fish even at low levels. In a healthy aquarium, colonies of bacteria live on surfaces (especially inside filter media) and convert:

• Ammonia → nitrite (still toxic)
• Nitrite → nitrate (less toxic, managed with water changes and plants)

This biological filtration takes time to establish in a new tank — often weeks, not days — and it relies on good oxygenation and a functioning filter.^{1, 4}

During cycling: what “normal” looks like

In the first month or so, it’s common to see ammonia rise first, then nitrite, then nitrate. One widely cited window for a tank to become “fully cycled” is around 4–6 weeks, though it can vary with temperature, stocking, and filter maturity.⁴

Practical testing rhythm for new tanks

• First 6 weeks: test ammonia and nitrite every 2–3 days (more often if anything looks wrong).⁴
• Once established: test every 1–2 weeks, and after any change to stocking, feeding, or filtration.⁴

Filtration and cleaning: keep the bacteria, remove the waste

Most “dirty water” problems come from a mismatch between waste input (stocking and feeding) and waste processing (filtration and maintenance). Good filtration is doing two jobs at once: trapping debris (mechanical filtration) and housing the bacteria that run the nitrogen cycle (biological filtration).¹

Routine that works in most freshwater tanks

• Partial water changes: often 10–25% weekly is a solid baseline, adjusted for stocking and feeding.¹
• Gravel cleaning: use a siphon to lift out settled waste during water changes.¹
• Filter care: rinse media gently in a bucket of tank water when it clogs. Avoid tap water, which can harm the beneficial bacteria.¹

Avoid “reset cleans” where everything gets scrubbed at once. That can strip out the biofilter and trigger an ammonia spike.

Algae control: treat the cause, not the colour

Algae is usually a symptom of excess light, excess nutrients, or both. You rarely need drastic treatments.

• Light: shorten the photoperiod and avoid direct sun on the glass.
• Feeding: cut back if food is hitting the substrate uneaten.
• Maintenance: keep up steady partial water changes and gravel cleaning.
• Wipe, don’t dose: clean algae from glass with an aquarium-safe sponge or magnetic cleaner. Never use soap or detergents.¹

Water conditioners and “supplements”: use sparingly and on purpose

Most tanks need far fewer additives than the labels suggest. The one product that is consistently useful for many households is a water conditioner that neutralises disinfectants in tap water.

Australian drinking water commonly uses chlorine and, in some systems, chloramine (a longer-lasting disinfectant). Both are harmful to aquarium animals, so treat new water before it goes into the tank, following the product directions.^{5, 6}

If you’re adjusting pH or hardness, do it with a clear reason (species requirements, measured instability) and move slowly. Sudden swings can be harder on fish than living in slightly imperfect water.

Things to avoid (including one myth)

• “Jousting” or deliberate fighting behaviour: this is not enrichment. It’s a welfare risk and can lead to injury, chronic stress, and infection.
• Overcleaning: scrubbing everything spotless often removes the biofilter that keeps ammonia and nitrite down.¹
• Overfeeding: excess food becomes waste fast, especially in warm tanks.

How often should I change aquarium water?

Many home aquariums do well with 10–25% weekly, paired with a light gravel clean. Stocking level, feeding, plant growth, and filter capacity can push that up or down.¹

How long does it take to cycle a fish tank?

A commonly cited timeframe is about 4–6 weeks for ammonia and nitrite to reach zero with nitrate production underway, but it varies. Test regularly rather than relying on the calendar.⁴

Should I clean my filter under the tap?

Usually no. Rinsing filter media in tap water can damage the beneficial bacteria that convert toxic ammonia into less harmful forms. Rinse gently in removed tank water instead.¹

Do I need an air stone?

Not always. If the filter outlet creates good surface movement, oxygen exchange is often adequate. If the surface is still, or stocking is heavy, extra aeration can help.^{1, 2}

References

1. RSPCA Knowledgebase — How should I care for my tropical fish?
2. RSPCA Victoria — Fish
3. RSPCA NSW — Caring for fish
4. RSPCA Knowledgebase — Why is water quality important when setting up a fish aquarium?
5. NHMRC — Australian Drinking Water Guidelines: Chlorine (physical-chemical characteristics)
6. NHMRC — Australian Drinking Water Guidelines: Monochloramine
7. NHMRC — Australian Drinking Water Guidelines: Chloramines
8. University of Florida IFAS Extension — Ammonia in Aquatic Systems