UNS Dual AIO 21 Gallon Rimless Tank

In this uns dual aio 21 gallon rimless tank review, the UNS Dual AIO 21 Gallon Rimless Tank earns the number four spot of eight in our best all in one reef aquariums guide. It is the best rimless AIO for aquascapers because low iron glass and a hidden rear filter leave the whole reef visible. Priced at $434.99, it holds 4.3 stars from 51 Amazon ratings. The tank measures 21 gallons and ships as a complete set: rimless tank, leveling mat, media riser tray, filter sponge, two bio bricks, submersible pump, outflow nozzle and back chamber lid. It runs freshwater or saltwater, so plant keepers and reef keepers can both use it. For a hobbyist who treats the tank itself as part of the display, that combination is hard to match.

Performance starts with the glass. Each pane is 91% low iron diamond glass with 45 degree precision cut mitered edges, and the silicone is deliberately minimal, which means you see coral color instead of a plastic frame. Behind the display, the triple chamber filter moves water through a coarse sponge, two UNS bio bricks and a media riser tray, so mechanical and biological filtration happen in one hidden column. The included submersible pump is built to run quietly, and the outflow nozzle returns that water across the display. Meanwhile, the leveling mat sits under the base and protects the glass on a stand that is not perfectly flat. In practice, this layout suits aquascapers who want to stack rock and place media their own way.

Value depends on what you already own. At $434.99, this UNS tank costs more than a BioCube 32, and it does not include a reef LED or a protein skimmer, so a full reef build pushes the total higher. By contrast, all in one tanks with built in lighting cost less up front but hide the reef behind trim and a fixed hood. That said, the UNS set includes the leveling mat, two bio bricks, the sponge, the riser tray, the pump and the nozzle, which trims the extras you must buy on day one. Even so, skip this tank if you want a preset schedule and plug and play lighting. If you enjoy tuning a system and want display grade rimless glass, this is the one to get.