Neon tetra care: plan a complete shoal

Recognising a neon tetra

FishBase records a body length up to 2.5 cm excluding the tail fin. The slim body, blue stripe and red markings help identify Paracheirodon innesi. In a tank, the whole shoal needs room to cross open water together and return to cover among plants.

Aquarium Industries, an Australian aquatics supplier, lists neon and cardinal tetras as separate species. The cardinal is Paracheirodon axelrodi. University of Florida research describes soft, slightly acidic water in the natural habitats and breeding of P. innesi. In an aquarium, regular tests help maintain suitable conditions without abrupt changes.

How large should the shoal be?

Aquarium Industries recommends at least six neon tetras. Eight to ten form a visible shoal in a suitable longer tank. Allow separately for the room and filter load of any other species. Introduce the neon tetras as a complete group.

Plants provide cover, with open routes between them. If one fish remains apart, hides persistently or misses meals, check water readings, tankmates and group size.

Set planting around open swimming water

FishBase lists 60 cm as a minimum aquarium length for neon tetras. A tank around 60 cm long and roughly 60 litres is therefore a practical starting point for eight to ten fish with no other stock. Planting along the sides and back gives shade while leaving the middle open. The filter should move water without pushing the shoal into a constant strong current.

Have planting and furnishings settled before fish arrive. A major rearrangement later removes familiar refuge. Introduce new fish gradually to the tank’s temperature and chemistry, keeping as little transport water as possible out of the established system.

Soft water and a mature filter

FishBase lists 20 to 26 °C for neon tetras. Keep a stable temperature within that range alongside soft, slightly acidic water. Measure temperature, pH and hardness before buying fish. The pH value describes acidity or alkalinity; general hardness mainly reflects dissolved calcium and magnesium salts. Any substantial change should be made gradually.

Cycle the biological filter without fish before stocking. Dose a designated aquarium ammonia product according to its instructions. Ammonia and then nitrite rise at first; after each measured dose, both should return to zero within the specified testing sequence. Regular tests after stocking show whether the filter can handle the shoal and its food load. Partial water changes remove dissolved waste.

Read more: Setting up a freshwater aquarium: tank, filter and water · Caring for an aquarium: watch the water, filter and fish

Use food that fits a small mouth

Finely broken complete flake or granule can be the main diet. Small live or frozen foods such as daphnia offer variety. Large pieces may sink untouched or be eaten only by bigger tankmates.

Small portions offered at several points reveal whether the entire group eats. Remove leftovers before they decay. A fish repeatedly missing food may face competition, illness or unsuitable current; check the observation alongside water readings.

Check the size and water needs of neighbours

OATA, the UK ornamental aquatics trade association, advises against keeping small tetras with fish large enough to swallow them. A seemingly calm large fish is still a risk if a neon fits in its mouth. Very active species may also keep the shoal driven into the plants.

Tankmates must share suitable temperature and hardness. A markedly harder guppy aquarium is not automatically a good home for neons. For any mixed stock, compare measured conditions, behaviour and the free space available to each complete group.

Read more: Six common aquarium fish and the differences that matter · Choosing aquarium fish that can live well together

Track colour, breathing and shoal behaviour

Temporary fading can accompany light changes or stress. Persistent dullness, unusual swimming, clamped fins, white patches or a fish separating from the shoal call for prompt assessment. Marked breathing difficulty or severe weakness needs immediate aquatic-veterinary help.

Check temperature, ammonia, nitrite and filter operation first. New fish may introduce disease; separate observation before they enter an established shoal reduces the risk to it. Dated images and test results assist veterinary assessment.