Ultum Nature Systems Prism Rimless Cube Aquarium 25TM Low Iron Review (2026)

Who this aquarium fits

The Prism 25TM suits aquascapers who want a small centerpiece tank with more vertical room than a standard cube, useful for layered hardscape, tall stem plants, or a moss-covered branch that needs height to look right. Its 5.9 gallon volume and roughly 10 inch footprint keep it compact enough for a desk, shelf, or office setup while still giving enough depth for a genuine planted layout rather than a bare nano bowl. Shrimp keepers and detail-focused aquascapers building intricate small-scale scenes are a strong match, since the low iron glass shows off fine hardscape and moss work with minimal color cast. It is less suited to keepers wanting a wide, shallow footprint for a sprawling carpet-style layout, since the Prism line's height comes at the expense of floor space compared to a standard cube of similar volume.

Build and dimensions

The tank measures about 9.84 by 9.84 by 14.17 inches, or 25 by 25 by 36 centimeters, holding 5.9 gallons of water with 5mm glass panels. It is built from ultra-clear, low iron glass with fully mitered edges and clear seamless silicone, a construction style that gives the glass a cleaner, more transparent look than standard green-tinted glass, particularly noticeable from the front and side panels of a rimless tank. The included lid also has mitered edges so it sits flush and inset into the top of the tank rather than resting loosely on top, and it has a center vent hole for gas exchange and to allow equipment cords or hoses through without lifting the whole lid. This construction quality reflects Ultum Nature Systems' general positioning as a premium rimless tank brand rather than a budget option.

Living with the taller shape

The Prism line's taller, narrower profile compared to a standard cube means the back corners sit further from the front glass relative to the tank's footprint, which makes reaching those corners with short tools noticeably harder than in a shallower tank of similar volume. Trimming stem plants or moss growing along the back glass, or adjusting hardscape tucked into a rear corner, generally calls for long tweezers and scissors rather than standard-length aquascaping tools, since a short tool may not comfortably reach the bottom-back corner without disturbing the front of the layout. The taller shape does reward careful vertical composition, since there is more room to build layered stone or wood arrangements that read well from a slight downward viewing angle, a look harder to achieve in a shallow tank.

How it compares with other UNS cubes

Against the larger UNS 30A all-in-one cube, which includes a built-in filtration chamber and holds about 7 gallons, the Prism 25TM is a simpler tank without integrated filtration, meaning external equipment such as a hang-on-back or small canister filter needs to be planned for separately. Compared to the UNS 20C, a standard 2.1 gallon low iron cube with a more conventional shallow-cube shape, the Prism 25TM trades some of that easy front-to-back reach for extra height and a larger 5.9 gallon volume. The Prism 30TM, the next size up in the same line, offers more volume for keepers who like the tall Prism shape but want more room than the 25TM provides.

Verdict and who should pick something else

This tank earns its score as a well-built, genuinely striking small aquarium for keepers who want a tall centerpiece display with premium low iron clarity and a lid designed specifically for the tank rather than a generic cover. It works best paired with long-handled aquascaping tools given the back-corner reach challenge that comes with its height. Choose a standard shallow cube instead if wide floor space for a carpet layout matters more than vertical room, or choose the larger 30A all-in-one if built-in filtration and more volume are priorities over the Prism's minimalist tall-cube design. Either way, budget for external filtration and heating separately, since this tank ships as glass and a lid only.

Frequently asked questions