What can I keep in this nano tank?

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What fish can be kept in a 45 x 45 x 45cm nano aquarium? Neale advises...

Q) My tank is a 45x45x45cm nano aquarium with a Fluval 206 external filter. I have medium-hard water so I’d like to check whether my choice of fish would be suitable. I’d like to keep three Marbled hatchetfish, four Otoclinclus, five Ember tetras, and a few shrimp and snails if I have anough space. What plants would work? I already have some Duckweed.

CHLOE ALLSWORTH

A) Neale says: By my reckoning, your tank contains around 90 l. While that’s a good amount of water for a starter community tank, the tricky bit about your aquarium is its shape.

The key thing about any tank is its surface area, whether measured at the top or bottom of the tank; i.e., the length multiplied by the breadth. The depth, by contrast, is only important insofar as it allows the chosen fish species enough room to swim comfortably without dragging their fins along the bottom.

Most standard fish tanks are longer than they are deep or broad, and that shape gives the greatest possible surface area. The surface area at the top of the tank is important because this is where gaseous exchange happens. Oxygen diffuses into the water from the air, while CO2 diffuses out, ensuring your fish have more oxygen to breathe. Cubic tanks compromise on surface area in favour of depth. While this can allow for some beautiful landscaping effects, it does mean that tanks with these shapes have to be stocked more conservatively. 

That said, the stocking density you suggest should be fine, but my concern would be that the small numbers aren’t ideal for the social species being kept. If this was me, I’d up the schools of hatchets and Ember tetras, and skip the Otocinclus. These catfish are fussy, needing well-oxygenated water to do well, and copious green algae to eat. While often purchased for ordinary community tanks, they don’t live very long under such conditions. Hatchets are more adapted to sluggish streams and ditches with copious vegetation and very soft and acidic blackwater chemistry. This isn’t what Otocinclus require, so I’d pick one or the other. Furthermore, larger groups of Embers and hatchets will feel more secure and look more peaceful, and in the case of the hatchets especially, we’re dealing with nervous and flighty fish that don’t handle stress well.

The riparian habitats that hatchets prefer will be thick with floating vegetation of all sorts, and I’d be looking at Amazon frogbit as a starting point, and the Duckweed would be good too. You don’t particularly need plants below the waterline, with bogwood, leaf litter, and a sandy substrate being far more authentic. Because hatchets are jumpy, an open-topped tank isn’t an option — or at least, not a very safe one — so while marginal plants with their leaves above the waterline would look good, I don’t think they’d work here. But you might try Hydrocotyle leucocephala and Sagittaria subulata as two relatively undemanding South American plants that could do well given sufficient light. Older plants of the latter can get rather large, so you might need to remove these periodically in favour of the smaller and more compact daughter plants that emerge from time to time.