For us aquarists, peeking over at our tank often results in a case of “light’s on, nobody’s home”. Many of our favorite critters are shy or nocturnal, preferring to spend the day wedged into safe crevices. Some only come out at night. But did you know there’s a way for your fish and invertebrates to stay comfortable even though they’re in full view? Enter the fish viewing cave!
What’s a fish viewing cave, anyway?
A large percentage of our aquarium fish and other livestock love to spend part, or even most, of the day in hiding. Given that larger, predatory creatures can’t get in, tucking oneself into cracks and caves in the rocks is one of Mother Nature’s most useful protective instincts. It’s also a bummer for reefers, because we can’t see our (often very expensive) critters when they’re comfortably napping inside a cave or tube! Yet we can’t remove these structures either, as this would cause them stress.
The solution is simple: find a way to view the fish and invertebrates while they’re inside their hides. That way, they can relax, and we can ensure they’re still alive and kicking—as well as view them up-close and personal.
Ever seen those ant farms that allow you to observe a colony of ants both above and below the substrate? Fish viewing caves are a little like that. Rather than a normal hide formed by stacking live rock, which only allows you to peer into the entrance (if that), these designs press against the tank glass and offer a complete view of everything that goes on inside.
Aquarium caves are almost always designed to be buried under the substrate, which prevents them from being eyesores and gives the fish an extra layer of security. Inhabitants get in through one or multiple entrances peeping out of the gravel. I bet a watchman goby and pistol shrimp pair would appreciate one of these! No more endless digging of hides.
Most fish caves are 3D-printed. This makes some aquarists suspicious (is that reef-safe?), but is actually a fantastic option that allows sellers to offer them for cheaper than ceramic. As I’ve discussed in my full post on 3D printing for your aquarium, safe materials—particularly PETG—exist, so you can totally use printed decorations and accessories like these even in your saltwater tank.
Choosing a fish viewing cave
Although 3D printed materials are not among the safety concerns when it comes to fish viewing caves for your reef, the design is. The main issue with some of these caves is that they’re not produced with water flow in mind; stagnant water can build up inside them and quickly becomes toxic. When the cave is subsequently disturbed, large amounts of ammonia and other dangerous compounds are released into the rest of the tank, which can crash the entire system.
Luckily, there are designs out there that do allow water to flow through freely. These have two exits, preferably sloping ones coming in from the sides rather than from the top. If you place them near a spot that gets plenty of movement, like a filter outflow, they’re unlikely to become death traps like the one-entrance designs. While looking for caves to feature, I came across the USA-based Lucky Critter Co, a small business whose “Two Hole Corner Cave” design looks perfect for use near an outflow.
Caves with (an) exit(s) placed at the top can also be safe, but you’d have to put a little effort into ensuring proper circulation. A simple air stone is enough to prevent disaster, though make sure its output isn’t so strong that your fish don’t want to enter the cave anymore!
Tip: In the last edition of Mari’s Must-Haves, I talked about reef magnifiers. These happen to be the perfect accompaniment to a fish viewing cave. Attach them to the glass in front of the cave to not just enjoy seeing your fish at all times, but to see every single detail with 3x magnification. Magnificent!
- The perfect Aquarium Underground Cave for many types of fish such as Pleco, Loaches, Corydora Catfish, Betta Fish, Shrimp and much more! Easy install by moving substrate out of the way placing against the glass and moving the substate back around the cave.
- While being a great place to hide it also provides an incredible viewing experience for the fish tank owner. This addition to an aquarium aquascape will give the ability to view fish in an entire new way in their natural environment.
- The Aquarium Underground Cave is made with aquarium safe plastic. It will also sink to the bottom of the aquarium so no need to try and bury it in the sand if not wanted.
- Size: 6" Length 6" Width 2.5" Height. Cave entrance 2.75" Length 2.25" Width
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