UNS Ultra Clear Rimless Cube Tank 2.1 Gallon 20C Low Iron Review (2026)

Who this cube fits

The UNS 20C suits aquascapers who want a genuinely small, highly detailed display, the kind of tank built around a single striking piece of wood or stone, a patch of moss, or a tight cluster of shrimp rather than a community of fish. Its 2.1 gallon volume and roughly 8 inch cube shape make it a common choice for desk setups, competition-style nano aquascapes, and photography-focused layouts where every element in the small footprint needs to be deliberate. Shrimp keepers building a dedicated breeding or display tank for a small colony are a strong match, since the tank's size keeps a shrimp population easy to observe up close. It is a poor fit for anyone wanting to keep fish beyond the smallest nano species, since 2.1 gallons offers very little stable water volume for most fish to thrive in long term.

Build quality and clarity

The tank measures 7.87 by 7.87 by 7.87 inches, equivalent to 20 by 20 by 20 centimeters, with 5mm glass panels and a leveling mat included in the box to help the tank sit evenly on a stand or shelf. It is built from Ultum's ultra-clear, low iron glass with a 45 degree mitered edge, a construction detail that removes the visible seam of a standard butt-jointed glass tank and gives the corners a cleaner, more finished look. Low iron glass in particular matters at this small size, since a tank this compact is usually viewed up close, where the greenish tint of standard glass would be more noticeable than it is across a larger display tank viewed from further away. The included leveling mat is a small but practical addition, since an uneven stand surface is more likely to stress a small rimless tank's silicone seams over time.

Living with a very small volume

A 2.1 gallon tank has very little water to buffer mistakes, meaning overfeeding, overdosing fertilizer, or a dead shrimp left unnoticed can shift water parameters far more quickly than in a larger tank with more dilution to absorb the same error. Regular small water changes and careful, minimal feeding become more important habits in a tank this size than in a larger aquarium with more forgiving chemistry. Equipment choice also matters more at this scale, since a heater or filter sized for a larger tank will visually dominate a cube this small and can also physically overwhelm the tight space available inside it, so nano-specific gear built for exactly this size range works better than scaled-down versions of standard equipment.

How it compares with other UNS cubes

Against the taller Prism 25TM and 30TM, which trade cube proportions for extra height and volume, the 20C keeps the classic even cube shape that many aquascapers still prefer for building a symmetrical or Iwagumi-style layout with a wide, easily reachable front-to-back footprint. Compared to the larger UNS 30A all-in-one cube with built-in filtration, the 20C is a bare tank requiring fully external equipment, appropriate given how little internal space a 2.1 gallon cube has for hidden filtration chambers. Against similarly sized cubes from LANDEN and HIRO Aquatics, the 20C's long track record and widespread availability of matching accessories like stands and lids give it an edge in ecosystem support even where core specs are comparable.

Verdict and who should pick something else

The UNS 20C earns its reputation as a dependable, clean-looking small cube for detailed nano aquascaping, backed by genuine low iron clarity, a mitered edge finish, and a practical included leveling mat. It rewards attentive maintenance and compact equipment choices, and it is not a tank to set up and neglect given how little volume there is to buffer mistakes. Choose a larger UNS cube or the Prism line instead if the goal includes keeping fish beyond the smallest nano species, or if daily maintenance time is limited, since bigger tanks are more forgiving of missed water changes. For a dedicated moss, Riccia, or shrimp display meant to be tended closely, the 20C remains a proven choice.

Frequently asked questions