How small can a reef tank go?

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Jeremy Gay advises a reader on what's required to set up small reef tank.

Q: What’s the smallest size of tank that would be feasible to run as a simple reef set-up? There would be no fish, just coral frags to grow on and maybe some reef hermits. What equipment would be necessary? Please can you also recommend some easy corals for a small set-up?

KEV BAGSHAW, VIA EMAIL

A: Jeremy says: With no fish, a tank for frags could be as small as 15-25 l, and it would only need a 25W heater, a 5W marine spectrum LED light and a pump to circulate the water. You would manage the water chemistry by doing frequent partial water changes, perhaps even daily. Small hermits would be fine in a tank that size too. But it wouldn’t hold many frags and the instability would make it more suitable for zoanthids or Xenia frags than SPS.

Up from that, I would consider a Fluval Evo at around 50 l. This comes with a light, pump and filter, but again that light is better suited to soft coral frags and LPS than SPS. You would also need phosphate remover and an auto top off. 

Moving up from that, I’d consider the Max Nano from Red Sea which comes with a good light that’s capable of growing SPS, has decent flow and a protein skimmer, which will help to raise oxygen levels and manage nutrients. It has a top-off unit built-in and you could add small fish as well as it has a volume of 75 l. 

But you don’t really need a protein skimmer on a frag tank with no fish, as it will just remove coral food from the water, so consider a bare tank like the Waterbox Cube or Peninsula. You could equip this with an AI Prime 16 HD Reef light, a small 2000 lph wavemaker, a heater, auto top off, and a phosphate reactor or algae refugium to manage nutrients. The Waterbox tanks range from 37-94 l. As it’s just for frags, surface area is more important than depth, as you just need somewhere to space them out, so they all receive enough light and flow. You could leave the tank base bare and use a three-tier acrylic frag rack to place the frags on.