Staying Safe & Salty in a Power Outage

If you've already read our freshwater breakdown of what to do when the power goes out over on the Aquatropic site, the general gist of this article will feel familiar: temperature, water quality, and oxygen all start slipping the moment the power dies, and the right response depends on how far into the outage you are. Reef tanks and marine fish-only or FOWLR systems run on a tighter margin than our freshwater friends. The details change somewhat so don't assume the freshwater playbook translates one-to-one.

The biggest structural difference is bio load density. A rock and sand bed teeming with bacteria, paired with corals, algae and inverts that never stop respiring, pulls oxygen down faster than a comparable freshwater setup, and saltwater itself holds less dissolved oxygen to begin with. Salinity also needs to be considered as any water you add to the aquarium for cooling, warming or oxygen needs to match the tank's specific gravity or it will change and become yet another stressor for your aquatic buddies.  Keep those two wrinkles in mind, and the rest follows a fairly intuitive escalation.

Under two hours:

A well-established marine tank (like yours) has some thermal and chemical inertia built into its water volume, rock and sand, so the first stretch of an outage is rarely an emergency. Note the time the power dropped, check your thermometer if that's part of your routine, and leave the tank alone otherwise. What we would spend this window doing is getting equipment ready rather than water changes; pulling out a battery-powered air pump, (if you don't have one, use this article as your sign to go buy one). For a tank carrying corals or other sensitive invertebrates, this single piece of gear matters more than almost anything else on this list, since those animals have essentially zero tolerance for a stagnant, oxygen-poor environment.

Two to six hours: get air moving before anything else

This is where a marine system starts to diverge from freshwater in urgency. Without a skimmer or return pump breaking the surface, oxygen exchange slows but oxygen usage doesn't. Densely populated aquariums can burn through oxygen very quickly, especially if the temperature starts to rise. Manual surface agitation like pouring tank water back in from a height or swirling a net through the water for a minute at a time is basically ineffective in marine tanks. Battery powered air pumps and / or battery powered powerheads running continuously and positioned to disturb the surface is the better fix if you have one. Once you're past a couple of hours, we'd also mix a modest batch of replacement saltwater, matched carefully to the tank's existing salinity and temperature before it goes anywhere near the tank. We're assuming here that you already have a water change worth of water sitting around and ready to use. This fresh batch of mix up is to replace that, or as a second water change(s) if the need arises. The value here isn't about nutrients (side benefit); freshly mixed saltwater is closer to full oxygen saturation than the stale water already sitting in the tank, so exchanging a portion of it functions as an oxygen top-up as much as anything else.

Six to twelve hours

Past the half-day mark, waste handling becomes the concern that catches people off guard. Smaller, more frequent water changes are the better tool at this stage than one large exchange, which risks shocking animals that may already be stressed; think 10 to 15 percent every couple of hours, always with saltwater matched to current temperature and salinity. The six-hour range is about the time you might want to think about insulating your aquarium with some blankets if the room with your tank is cooler or warmer than you keep the water temperature. Heat is a bigger problem than cold. Almost everything in your reef system can manage a few hours of temps in the low 70s and maybe even high 60s. However, a jump into even the low 80s might kill everything. For those of you who suffer from summer storm power outages (looking at you gulf coast) find a way to keep that tank cold!

Past twelve hours

Once an outage stretches beyond 12 hours, the plan shifts from managing decline to active triage. Honestly, the best thing here is a small generator or large battery backup. If you live somewhere that has more than a single power outage a year, buy back up power. A small generator will cost you less than your reef lights and a battery backup not much more. The nice thing about the battery backup, is you can run it in your 4th floor apartment. If you've been having a power outage for 12 hours, you can pretty well guarantee that every generator system near you has been sold to your neighbors, so think about this ahead of time. If you haven't thought about this in time, try to keep the room that the aquarium is in as close to normal aquarium temperature as you can. Next, run any flow device you can, from air stones to powerheads, because corals depend on water movement for gas exchange in a way that free-swimming fish don't. If it's winter where it gets cold (looking at your upper Midwest / east coast) when your power goes out, you may need to warm your aquarium. Keeping the house warm with back up heat sources like wood fires etc. if you have that option will keep your aquarium warm too. If you have a way to heat up water like a camp stove outside, you can warm some of your pre-mixed water for your water changes to help hold the line, but add it slowly, since sudden shifts in aquariums is no bueno. Seriously, if your reef tank is 55 gallons or bigger, go and buy a small generator or battery backup. You just need something to keep the filtration (and maybe heater / chiller) running, it doesn't have to be monster construction site generator; your sump setup might have cost you more than the one you need.

What carries over from the freshwater article is the underlying principle: a water change during a power outage isn't just about nutrients, it's primarily a tool for managing oxygen and temperature. The saltwater-specific twist is that it only works if salinity comes along for the ride; mismatched water solves one problem while creating another. Keep a few gallons of correctly matched saltwater on hand. You should always have enough water mixed for your next water change. Mix a fresh batch as soon as you use the last batch to change the water. You should always, always, always have a battery powered air pump and a few batteries too, (or just go and get a generator, seriously, you might have a fish that costs more than a small one). If you're well prepared, a marine tank can ride out a surprisingly long outage without lasting damage, provided someone is actually paying attention to it, not doing too much, but also not just hoping for the best. Happy Aquarium Keeping!