Ultum Nature Systems Ultra Clear Rimless Aquarium, 15.1 L 25C Cube with Low-Iron Glass

The Ultum Nature Systems Ultra Clear Rimless Aquarium is a 4-gallon fish tank for aquascaping, made with 91% clarity low-iron glass and 45° mitered edges.

• 91% clarity, low-iron glass — gives a clear view with very little green tint.
• 45° mitered glass edges — create uninterrupted-looking corners.
• 5–12 mm glass thickness — provides the specified thickness range.
• German-made aquarium silicone — bonds the glass for moisture-rated durability.
• 25C cube, 9.84 × 9.84 × 9.84 in (25 × 25 × 25 cm), 4 gallons — a compact format for aquascaping.
• Black leveling mat included — adds a non-slip base beneath the aquarium.

This rimless tank is made for people building an aquatic landscape who want the glass to keep attention on the view inside. Its golden-ratio-inspired dimensions allow extra room to create perspective and show depth, while its minimalist appearance suits display in a room as well as an aquascaping setup.

What is the Ultum Nature Systems aquarium designed for?

It is designed for aquascaping, with proportions intended to help create a sense of depth and perspective. Rather than following conventional rimless aquarium sizing, the design considers the aquascaper’s layout and applies the golden ratio. The result is a tank format that gives the arrangement visual space while keeping the overall look minimalist.

• Designed with aquascaping in mind.
• The golden-ratio approach shapes the tank proportions.

How clear is the glass, and how are the corners joined?

The tank uses extra-clear, low-iron diamante glass with 91% clarity and 45° mitered edges. Low iron reduces the greenish or bluish cast found in ordinary glass, helping aquatic plants and other elements appear closer to their natural colours. The angled edges meet with a less visually prominent corner line, supporting an open view into the aquarium.

German-made silicone formulated for aquarium construction bonds the panels. The adhesive is rated for moisture and durability, making it suited to the aquarium’s wet environment.

• Diamante glass has very little residual green colour.
• The aquarium silicone is made in Germany and designed for aquarium use.

What size is the 25C aquarium, and what comes with it?

The 25C is a cube measuring 9.84 × 9.84 × 9.84 in (25 × 25 × 25 cm), with a stated capacity of 4 gallons. A black leveling mat is included to sit under the tank. Its non-slip surface helps support the base and reduce shifting or slipping.

The mat is intended to provide a suitable base for the aquarium rather than requiring a makeshift cut-to-size mat. The cube dimensions give buyers a clear footprint to compare with the space planned for their aquascape.

• Model: 25C cube.
• Included accessory: black leveling mat.

This aquarium suits aquascapers and fish keepers looking for a compact rimless display with low-iron glass, angled glass joins and a mat for the base. It is a 4-gallon cube designed to make the aquatic layout the focus.

Read our guide: Aquascaping a freshwater tank: substrate, stone, wood and light