The title of this post is a bit misleading. What I mean by “building” isn’t exactly synonymous with turning raw material like clay, for example, into something that resembles a cave. This post is more about using various aquarium-safe objects for caves and breeding structures.
Let’s start with the simplest of components. Rocks. You can “build” caves out of almost any type of rock. However, not all types of rocks are suitable for aquariums. That’s a post for another day, so if you want more information about which types of rocks are aquarium safe, do a Web search for that.
Okay, onto rocks and cave building. As a general rule, rocks can make great caves because rocks themselves come in all different shapes and sizes. Personally, I like river rock. These are easy to acquire, typically have a smooth surface, and come in various color shades and sizes. I like to use the flatter varieties because they stack nicely.
Depending on the fish you keep, your caves may need to be very small or quite large. Also, think about the purpose of the cave you’re wanting to build. If you just want to build something as a place of refuge for your fish, it doesn’t have to be elaborate. It also doesn’t even have to be completely closed off with only one entrance.
On the other hand, if you’re building a cave for breeding, it might need to only have one entrance and it might even need to be really tight for the female. Some species, like A. calvus like tight quarters and only one way in/out. Other cave/crevice spawning species are quite picky about where they lay eggs.
Depending on the purpose of the cave, another natural component is wood. There are lots of different wood types that are safe for aquariums, but like rocks, that’s a post for another day. Unlike rocks, wood tends to breakdown in water over time. Yes, limestone rocks and some others will degrade over time, but you’ll probably be dead before you notice it. Wood is different. Many types of wood breakdown pretty quickly. A lot of this depends on the water in the tank too. Furthermore, many types of wood leach tannins into the aquarium, discoloring the water and affecting your water parameters unless you’ve got filter media to catch it.
Though many purists loath the look of anything artificial in an aquarium, many folks use PVC and ceramic components. A single PVC piece can serve as a cave or you can connect pieces together. I use PVC elbows sometimes – 45, 90, and 180 degree varieties. I sometimes also use simple T connectors. The size you need depends on the size of fish you’re targeting and the purpose of it. If just shelter, it only needs to be large enough for the target fish to get in and out. If you have a tank of mixed size predatory species, having caves that only the smaller species can fit into can be very advantageous.
Speaking of artificial components, one of my cichlid friends, Pam Chin, loves ceramic pagodas, castles, and such. Fired clay products are used by many aquarists also – for breeding, shelter, etc. These include pots, tubes, domes, bowls, etc.
You should consider using any combination of the above as well. There are no rules about what you can combine. After all, it’s your tank. Use what works and what you like. Use your imagination. Stack things. Connect things. Your fish will let you know if they like what you provided or not. Who knows? You may get a pair of fish to breed simply by arranging your objects a certain way. Just make sure whatever you put in the tank won’t leach any dangerous chemicals or otherwise cause harm to your fish.