The beginners guide: picking your first tropical aquarium fish


Filling an empty glass box with water offers a surprising amount of excitement for the new aquarist, but it doesn’t compare to the enjoyment of adding your first few fish.

As ever, there is planning to do before taking a trip to a local aquatics shop and buying fish. Most importantly, your aquarium should be matured by completing a fish-less cycle, or you should have some mature bio-media ready, or recently added.

For more on these methods, see:   

Image above: White Cloud Mountain minnows are a popular choice


The best first fish for you depends on a few variables. The most significant variable is your water source. Mains tap water is obviously the most common source, but some will be using water from a bore-hole or maybe rainwater.

Whatever the source, you need to know it’s make-up. Water hardness is of most concern when it comes to fish selection. Hardness refers to the volume of dissolved minerals in any given sample of water. Most of the UK is subject to moderately hard tap water, but it could be super hard or soft, depending on where you live.

For more on what hardness is, see:

Image above: A mixed, soft to slightly hard water community tank


As a beginner with hard, or moderately hard tap water, it is advisable to research fish which will suit your conditions – softening hard water is not in a beginners remit. Don’t worry; you have plenty of options still!

If you have soft or softish tap water, you have more options. Soft water fish will be suitable and advisable (as soft, acidic water renders ammonia less harmful – in the form of ammonium). Still, if you prefer hard water fish, it’s simple to add extra hardness with commercial buffering products.

The next variable is how you mature the aquarium. A big bonus of the fishless cycle is that you start with a mature aquarium, or as near to it as possible. This allows you to put a larger number of fish in initially, and you don’t have to stick to hardy species only.

Image above: A group of Danio tinwini


If you are adding mature bio-media, then only add a few fish initially. And make them hardy species, because there may be slightly elevated waste levels somewhere along the line, as you add more fish.

The following suggestions are based on a 60cm, 70ltr tank. I have avoided fish which may breed easily and over-fill an aquarium, and fish such as loach and catfish, which often require a more ‘lived-in’, mature tank. All the following fish are peaceful, quite easy to obtain and simple to feed with prepared foods.

Image above: X-ray tetra, Zebra danio and Gold barb


Hardy, neutral to hardwater species:

Zebra danio, Brachydanio rerio. Also leopard and pearl danios.

Cherry barb, Puntius titteya

Chequered barb, Oliotius oligolepis

Gold barb, Barbodes semifasciolatus

X-ray tetra, Pristella maxillaris

Image above: Harlequin rasbora, Red-eye tetra and Glowlight danio


Hardy, slightly hard to soft water species :

White Cloud Mountain minnow, Tanichthys albonubes

Harlequin rasbora, Trigonostigma heteromorpha

Glowlight danio, Celestichthys choprae

Goldring danio, Brachydanio tinwini

Many tetra – including Red-eye, Cardinal, Emperor, Ember, Lemon, Phantom tetra, Rummynose, Black neon tetra and more

Image above: Forktail blue-eye, Dwarf emerald rasbora and Neon dwarf rainbowfish


Other neutral to hardwater fish:

Forktail blue-eye, Pseudomugil furcatus

Neon dwarf rainbowfish, Melanotaenia praecox

Emerald dwarf rasbora, Celestichthys erythromicron

Image above: Lyretail killifish, Ram cichlid and a Dwarf pencil fish


Other slightly hard to soft water fish:

Killifish, Aphyosemion and Nothobranchius species

Honey gourami, Trichogaster chuna

Ram cichlid, Microgeophagus ramirezi

African butterfly cichlid, Anomalochromis thomasi

Pencil fish, Nannostomus species


These are by no way exhaustive lists. Though many aquarists and shops will suggest that many soft water fish will adapt happily to harder conditions (especially farmed fish), do they have evidence for this? It is highly possible that, when kept in hard water  conditions, excess minerals are slowly causeing biological stress (alkalosis).

For the best health, fish should be kept in the conditions they have naturally adapted to. Keeping hard water species in soft water is far more harmful, or let's say, more quickly harmful at least.