FAQ: Plants for fish

Yes, healthy fast-growing plants use up nitrates, phosphates and light, leaving less food for algae. Dense planting, floating plants and lighting balanced with fertilising help the most.

In a new tank the plants have not rooted yet and grow slowly, and the biological balance has not settled, so algae easily take the nutrients. For the first weeks shorten the light period, change water more often and plant more fast-growing species.

On tough leaves such as anubias, algae can be gently rubbed off with fingers or a soft brush. Heavily covered leaves are best cut off, and over time reduce the light, adjust fertilising and bring in algae-eating shrimp or snails.

Some algae removers can harm sensitive plants, shrimp or snails, so read the label carefully before use. For a lasting result, removing the cause matters more: an imbalance of light, fertiliser and CO2.

A brown coating that wipes off easily is usually diatoms, which are typical of new tanks and water containing silicates. They usually disappear within a few weeks as the tank matures, and snails and some fish happily eat them.

Black beard algae is a dark, tufted red alga often linked to fluctuating CO2 and weak flow. Cut off affected leaves and ensure stable CO2, good water movement and regular water changes.

Yes, plants use nitrate to grow, so less of it builds up in a heavily planted tank. Still, plants do not replace regular water changes, and fast-growing and floating plants absorb nitrates best.

Yellowing leaves often point to a nutrient shortage: old leaves yellow when nitrogen or potassium is short, young ones when iron is short. Lack of light or old leaves dying naturally can also be the cause, so watch which leaves change colour.

Small pinholes in older leaves often point to a lack of potassium, while larger irregular holes can come from fish or snails nibbling the leaves. Check that you fertilise enough and watch what in the tank is eating the plants.

Cryptocorynes are known for melting, when after being moved or after a sudden change in water parameters their leaves go soft and die back. Leave the roots alone, remove the rotting leaves and wait, as new leaves usually grow within a few weeks.

Plants usually stall when they lack light, CO2 or a particular nutrient, or while they are still adjusting after planting. Check the light period, fertilising and water parameters, and change one thing at a time so you can see what helped.

Stems rot when they are damaged during planting, pinched by a metal weight, planted too densely, or when the substrate lacks oxygen. Cut off the rotten part, replant the healthy top and leave more space between stems.

Pale, white or see-through new leaves often point to a lack of iron, manganese or other micronutrients, sometimes also a lack of CO2. Try an all-in-one fertiliser with micronutrients and watch whether new leaves grow in with a healthy colour.

An anubias rhizome usually rots when it is buried in the substrate, damaged or has been kept in poor conditions for a long time. Cut the soft rotten part back to healthy tissue and attach the rest of the plant to a rock or wood above the substrate.

Plants themselves do not make fish ill, but plants from another tank can carry parasites or pathogens. That is why new plants are worth quarantining or buying in vitro, and if you see signs of sick fish, contact a vet.

Some fish treatments can harm plants, shrimp or snails and disrupt the filter bacteria. Agree any treatment with a vet, follow the label and, where possible, treat sick fish in a separate quarantine tank.

In hard water, especially when plants grow fast without CO2, a whitish lime crust can form on the leaves. It is harmless to plants but reduces light, so it can be wiped off; CO2 or softer water reduces the problem.

Replanted plants go through stress: some leaves may die back while the roots adjust to the new substrate and water. Move plants as rarely as possible, do not break the roots and do not expect fast growth for a few weeks afterwards.

Leggy plants with sparse leaves usually point to a lack of light, sometimes also to temperature that is too high. Move them closer to the light, improve the lighting and trim the leggy parts so the plants branch more densely.

Partly: what matters is whether old or young leaves change, and whether holes, spots or paleness appear. The signs often look alike, though, so it is worth assessing lighting, CO2 and fertilising together and checking water parameters with tests.