FAQ: Water Care for fish

Treated water at the right temperature does not harm them, as they mostly live in the filter and on surfaces, not in the water. Unconditioned tap water or combining the change with a heavy filter clean can do harm.

Usually pouring stirs up the substrate or fine particles, which settle within a few hours. If it turns milky and lasts, it may be a bacterial bloom or microbubbles from the tap, which clear within a day.

Gases dissolved in cold tap water come out as bubbles on the glass, plants and decor as it warms. It is usually harmless and clears in a few hours, and water prepared and left to stand beforehand reduces it.

Turtles foul the water heavily, so it is changed often, sometimes half or more, with regular vacuuming of the bottom. Since turtles breathe air they tolerate larger changes, but the temperature must be right and the water conditioned.

In planted tanks dosed with fertiliser, 30–50% weekly changes are common to prevent build-up and algae. It depends on the fertiliser system, so follow the manufacturer's recommendations.

Green water is caused by free-floating microscopic algae that multiply fast with lots of light, especially sunlight, and nutrients. Shorten the lighting, keep the tank out of the sun, feed less and change water, and a UV steriliser clears it quickly.

A yellowish or brownish tint usually comes from tannins in driftwood, leaves or peat. It does not harm fish and some even like it, but if you want clear water, activated carbon in the filter and regular water changes help.

Greyish cloudiness is often fine substrate dust, especially in a new tank or after the gravel has been disturbed. It settles within a few days, and filter floss clears it faster. New substrate is worth rinsing well before use.

Clarifiers clump fine particles into larger flakes that the filter catches or that settle out. They improve clarity quickly, but they do not fix the cause of cloudiness, such as overfeeding or a bacterial bloom.

Used as directed they are generally safe, but overdosing can lower oxygen or clog the filter. For sensitive animals like shrimp, choose a product the manufacturer states is suitable for invertebrates.

Surface film is made of proteins, fats from food and bacteria, especially when the surface is still. It hampers gas exchange, so a filter outlet that moves the surface, a surface skimmer or lifting it off with a paper towel helps.

Foam that does not disappear means the water contains a lot of dissolved proteins and organics, for example from overfeeding, or soap or other substances got in. Change part of the water, cut back on feeding and check your equipment is clean.

A healthy tank smells earthy, while a rotten or sulphur smell points to decaying matter, a clogged filter or oxygen-free pockets in the substrate. Remove debris, clean the filter, vacuum the substrate and change part of the water.

Algae thrive on lighting that is too long or too strong, direct sunlight, excess nutrients from overfeeding and infrequent water changes, and too few live plants. Balancing these factors usually works better than any single product.

Chemical algae treatments can kill algae quickly, but some harm shrimp, snails or sensitive plants, and dying algae reduce oxygen. Use as directed, increase aeration and deal with the cause of the algae at the same time.

About 6–10 hours of light a day is the usual advice, on a timer to keep it consistent. If algae are spreading, cut the lighting by an hour or two and check the plants are still growing well.

Phosphate mostly comes in with fish food, sometimes with tap water, fertilisers or certain water products. It builds up with heavy feeding and infrequent water changes, so moderate feeding and regular changes help.

They are slimy, often blue-green films on substrate and plants with an unpleasant smell, spreading in poorly circulated, nutrient-rich water. Manual removal, better flow, water changes, shorter lighting and moderate feeding help.

Brown coatings, usually diatoms, often show up in new tanks when the water is rich in silicates and the balance has not settled. They usually fade within a few weeks, helped by cleaning, water changes and algae-eating animals such as snails.

The warmer the water, the less oxygen it holds, while the fish's metabolism and oxygen demand increase. So on hot days or in tropical tanks good surface movement and sensible stocking are important.