FAQ: Water Care for fish

In water, ammonia exists in two forms: toxic free ammonia and much less harmful ammonium. At low pH there is more ammonium, and as pH rises the toxic form increases, so most tests show the total and pH helps judge the danger.

Yes, uneaten food rots and releases ammonia, so overfeeding is one of the most common causes of poor water quality. Feed only what the fish eat in a few minutes, and remove any leftovers.

They can cut ammonia quickly and help in an emergency, but they do not fix the cause. You also need to feed less, check the filter, change water and avoid overstocking, otherwise the ammonia will rise again.

If tap water is treated with chloramine, the conditioner breaks it down and releases ammonia, which the filter bacteria then consume. Ammonia can also rise if the filter was heavily cleaned or the substrate stirred at the same time.

It is worth testing your tap water's pH, hardness, nitrate and ammonia at least once so you know what goes into the tank. That makes it easier to tell whether problems arise in the aquarium or come in with the new water.

During cycling it is worth testing ammonia and nitrite daily or every other day to follow progress. Once they are steadily at zero you can test less often, and more often again when you start adding fish.

In a new tank, milky cloudiness is often a bacterial bloom while the biological balance settles. It usually clears within days or weeks; light feeding and patience help, and sometimes a bacteria starter.

Some plant substrates, especially active soils, release ammonia in the first weeks. This is normal and speeds up cycling, but hold off on fish and shrimp, change water more often and test ammonia until it falls.

First test ammonia, nitrite, pH and temperature, and check that the filter and heater work and no household chemicals or sprays got into the water. Remove the dead fish, change part of the water and, if the cause is unclear, consult a vet.

Yes, a decaying body releases a lot of ammonia, and in a small tank this quickly worsens water quality. Look over the tank daily, remove dead animals and rotting plant parts at once and test for ammonia.

Nitrite stops fish blood from carrying oxygen, so fish suffocate even when the water has enough oxygen. In a healthy, cycled tank there should be no nitrite, and any amount shows the biological filter is not keeping up.

Change part of the water with treated water, cut back on feeding, increase aeration and test nitrite daily until it falls to zero. Some fishkeepers use a small amount of salt, which reduces nitrite's effect, but only do this after advice from a specialist.

Fish gasp at the surface, breathe rapidly, are sluggish and their gills may turn brownish. These signs mostly appear in a new tank or after a filter problem, so test the water at once and contact a vet if needed.

Nitrate is the end product of the nitrogen cycle, far less toxic than ammonia or nitrite, but in excess it harms fish over time and feeds algae. It is often kept below roughly 20–40 mg/l, and lower for sensitive fish and shrimp.

The main way is regular partial water changes. Moderate feeding, sensible stocking, vacuuming the gravel and live, fast-growing plants that use up nitrate also help. Nitrate-removing resins can add to this but do not replace these habits.

Your tap water may already be high in nitrate, the tank may be overstocked, the fish overfed or a lot of muck may be building up in the gravel and filter. Test your tap water, and if it is high in nitrate consider reverse osmosis water or more plants.

No, nitrate is a nutrient for plants, so heavily planted tanks sometimes even have it added with fertiliser. Having no nitrate at all can stall plant growth, so balance matters rather than zero.

The key ones are ammonia, nitrite, nitrate and pH, while hardness (KH and GH) matters especially for shrimp, cichlids and planted tanks. It is also worth glancing at the thermometer daily, as temperature is one of the main factors in fish health.

Test strips are quick and convenient and show several parameters at once, but they are less accurate and sensitive to moisture. Liquid tests take longer but are usually more accurate and cheaper per test, so they are often used to pin down problems.

Rinse the test tube with tank water, fill exactly to the mark, hold the dropper upright and add the stated number of drops, shake well and wait the stated time. Compare the colour in daylight against the white background of the chart.