Keeping a Coldwater Marine Aquarium

Marine aquarists have always had access to temperate species. In fact, in the days before improved packaging/shipping procedures allowed for the massive import of tropical species that we enjoy today, most saltwater aquarium livestock originated from temperate waters. Catalina gobies, waratah anemones, garibaldi damsels… At least half of the seahorses… The coolest boxfishes… Anyone who thinks that coldwater tanks are boring or lack color is totally full of it.

This article explores the possibilities–and unique requirements–of coldwater marine aquaria.

Not for the weak

For sure, some crazy amazing coldwater displays have been put together over the last few years. They demonstrate that recent technological advancements in water pumps, dosing gadgets, etc. have increased the potential for coldwater systems every bit as much as they have for tropical systems. But they also reveal that coldwater systems have their own big demands. 

The first such challenge is (unsurprisingly) temperature control. Quite simply, it’s a lot easier to heat water than it is to cool it. And when you need to keep your water temps down to 55F, or even cooler, you’re not going to get by with a crappy homemade chiller or by cranking up the AC. In short, you’ll have to invest in a big, powerful aquarium chiller. If you’re too cheap to understand “big” and “powerful,” you won’t buy the right chiller, and if you don’t have the right chiller, your coldwater marine aquarium will be a disaster.

The second such challenge is insulation. Yes, a well-insulated tank seriously lightens the load on a chiller. But it also helps to prevent sweating. Sweating? Yes, that’s when moisture in the air condenses into fog and droplets on the outsides of a cold aquarium. At best, sweating jacks up the view of your display; at worst, it ruins cabinetry, equipments, floors, etc. Thankfully, it can be avoided by staying away from thin glass and instead opting for thick acrylic. Some coldwater marine aquarists have also avoided this issue with double-pane glass tanks (ever see one of those Marineland lobster tanks on Craigslist?).

A third challenge is cycling. Because the nitrifying bacteria commonly used in aquaria proliferate at a much slower rate in cold water, establishing the nitrogen cycle takes longer and requires a bigger biofilter. When you throw in the fact that coldwater tanks generally get fed a lot more, you’ll understand why many recommend a biofilter that offers roughly twice the capacity as for a comparable tropical set-up. To save on space while meeting this hefty requirement, one might suggest a highly efficient biomedium with a very high surface-to-volume ratio (e.g. MarinePure). Fortunately, you can speed up the process (assuming no livestock has been added) to start with a warmer temperature. In this case, you may crank up the temp to 82F, add a big dose of inoculant and fuel (e.g. Aquarium Cycle Kit). Simply lower the temp as desired after cycling is complete.


Alright, maybe there’s one more challenge–sourcing livestock. You can’t just run over to PetCo and find a huge selection of coldwater marine aquarium animals. These animals are usually rare in the trade and quite hard to find. Only a few online dealers specialize in temperate species. Sometimes, you really just end up snatching whatever you can find. For those aquarists who enjoy the pursuit of unusual species, it may actually be a pleasure to hunt down and obtain those special gems that no one else has. For tons of great information about popular temperate fauna and leads for retail sources, check out:

There are so many great temperate fish and inverts that it is impossible even to present an overview here. There are many fish families, for example, that many tropical aquarists aren’t even familiar with–pricklebacks, gunnels, triplefins, rockfishes, lumpsuckers, sculpins, surf perches, and so on. And the invertebrates… if there may be a niche for “monster” inverts, it is in coldwater. These are the biggest starfish, cucumbers, octopuses, chitons, crabs, etc. that you’ll ever find. And some of the most gorgeous sea anemones that you’ll ever see! Just check out some of these beauties:

Aquarium care

There are coldwater clownfish, damsels, angelfish, butterflyfish, gobies, blennies, wrasses, eels, etc. and their care is pretty much analogous to that of their tropical counterparts. In many instances, the temperate “versions” of these fishes are comparatively hardier, easier to feed and more disease-resistant (so long as they don’t get too warm!). The corals, sea anemones and clams are also hardy, though they are typically non-photosynthetic and therefore must be fed often (at least lighting is often of little concern in these systems!). 

Given the generous feeding, detritus and excess nutrients can become a concern. Like in a tropical system, these issues can be addressed with a planted refugium. Sea lettuce loves cooler water and is a great macroalgae for coldwater refugium use. Coldwater refugia can support huge numbers of Tigriopus (technically a temperate copepod), which help to clean up detritus and serve as an excellent live food for numerous corals and small fishes.

For those that want to try something new (or something super old-school, depending on how you look at it), operating a temperate marine system may be the most fun experience you’ll ever have in the hobby. And, as you discover new fascinating and eye-catching species, you’ll come to see the world as an even bigger and more beautiful place.

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