The Ultimate Guide to Marine Invertebrates for Nano Tanks: What You Need to Know

Marine invertebrates are a great addition to any saltwater aquarium. They're not only fun to watch, but they bring practical benefits to your tank, too. From tiny snails cleaning algae off your tank's wall to hermit crabs scavenging for leftover food, these creatures can play a vital role in your tank's ecosystem. But with so many species available, choosing and caring for your tank's newest inhabitants may feel daunting! But don't worry. Raising inverts is also fun and rewarding, which more than makes up for the preparation you may need to do.

Finding the right invertebrates for a nano tank involves understanding which species work best in a smaller environment and researching how they interact with everything from corals to your other fish. This guide will provide insights to help you create a thriving underwater habitat.

Note: While corals are also considered invertebrates, this guide will focus on non-coral invertebrates for your saltwater tank.

Why Invertebrates Are a Vital Choice for Saltwater Aquariums

Invertebrates are fun to watch, but they have a practical benefit for your saltwater aquarium.

Invertebrates make a great "clean-up crew" for saltwater tanks of any size. They hunt through your aquarium, looking for tasty organic matter you'd consider a nuisance, like algae, waste, or leftover food. Not only does this make your tank look cleaner, but their taste preferences also boost your filtration and keep your water quality stable.

Snails, for example, work day and night, eating microalgal film from rocks and glass. Hermit crabs eat algae off your rocks and the leftover food from your substrate.

Invertebrates Great for Nano Tanks (and Which to Avoid)

Not all invertebrates are created equal when it comes to nano tanks.

Research each species before you add it to your aquarium. Some you might find intriguing will grow too large to be sustainable in a nano tank. For example, tridacnid clams might start small but will eventually be too big. Sand-sifter starfish are similar. They love searching your substrate for leftover food but will starve in a nano tank after they grow larger. And sea cucumbers should generally be avoided by anyone but a very experienced aquarium hobbyist since they can release a toxin when injured, which could kill your fish.

Examples of invertebrates that can do well in a nano tank include:

• Peppermint shrimp: They stay small and are generally easy to care for, which is great for nano tanks.

• Dwarf hermit crabs: They're great at scavenging and cleaning your tank. One good choice is the scarlet hermit crab, which stays small and is also reef-friendly. Another fun choice is the electric blue dwarf hermit, which does best in pairs since they're social. You do need to provide lots of pretty empty shells so they don't steal shells from your snails or other hermits!

• Small snails: They can help keep your algae under control, but you only want the species that remain small, like Astraea snails. Another good choice is the bumblebee snail, which has beautiful stripes. Don't choose Trochus or Tectus snails because they'll eventually need more algae than your small tank can provide. You also want to avoid any small snails that eat other snails, like the Ilyanassa obsoleta snail.

• Small crabs: The emerald crab is an example of a small crab that loves to scavenge. It even eats bubble algae, which not all species bother consuming.

• Lettuce nudibranch sea slug: This one is only a good fit for larger nano tanks of at least 20 gallons in size. It eats annoying hair algae, but it's too fragile to be a good choice for beginners.

Note: If you have corals in your nano tank, make sure your invertebrates are reef-safe. Some inverts are known to eat or damage corals.

Choosing Healthy Invertebrates

When you're at a pet or fish store choosing invertebrates for your tank, watch for telltale signs that they're healthy.

For example, crustaceans should have an overall healthy appearance and not just appear "listless" on the bottom of the tank. Constantly moving mouthparts can be a sign of a healthy crustacean.

When choosing snails, look for ones firmly attached to the tank's glass or rocks. Just remember, since some snails are more active at night, they may not be actively moving while you're watching them.

When do you add invertebrates to your nano tank?

If you have a nano tank, inverts will be the first live animals you add after substrate and rocks. Your tank should be fully cycled, and the water condition — including ammonia, nitrite, and nitrate levels — stabilized. A water kit can help you make this determination. (Check out our comprehensive guide to water testing for more details.)

Once these conditions are met, wait until you see algae growing before you add your first invertebrates so they can start cleaning off that algae right away. The first algae you'll likely see are diatoms (a brown, powdery algae). At this point, introduce some hardier invertebrates like Astraeas snails, which feed off the diatoms. If you have live rock, your tank will have more kinds of algae from the get-go, so you can add hermit crabs too.

Don't add your scavenger invertebrates until you have fish and corals in your tank, so they have plenty of leftover food and waste to eat.

Remember, after you add your invertebrates, you still need to keep a close eye on your tank's water quality and stability. Invertebrates (like many other saltwater residents) can be sensitive to temperature, salinity, and pH changes.

Avoid Fish That Will Eat Your Invertebrates

If you want a thriving invertebrate colony, only choose fish that will leave your clean-up crew alone. And make sure the fish won't grow too big for your nano tank.

Avoid angelfish, for example. They may be good at picking algae off corals, but they're also big-time predators that love eating invertebrates. In fact, they may only ignore your little inverts if they're kept well-fed in a large tank with live rock. One of the only exceptions is the Japanese swallowtail angelfish, which doesn't like feasting on invertebrates. (However, this fish grows to six inches, so leave it for the larger tanks.)

Examples of reef- and invertebrate-safe fish you might consider include clownfish and shrimp gobies.

Some nano tank owners choose to skip fish altogether so they can have a wider variety of invertebrates in their tank.

Feeding Invertebrates

How you feed your inverts will depend on the species you keep. Planktivores eat phytoplankton and planktonic food suspended in the water. Algivores, just like their name sounds, eat naturally growing algae. Detritivores scavenge for decaying organic matter and leftover food.

Some inverts will find plenty of food naturally if you have fish you're feeding or algae that's growing on rocks and corals. Others will need a little extra food from you. You can get food at pet stores made specifically for inverts, like sinking crustacean pellets, seaweed to graze on, freeze-dried plankton, phytoplankton for filter-feeding inverts, and more.

You may need to find a balance between feeding and cleaning. Sand-sifting stars, for example, sift through sand looking for food, but they might starve if you clean the sand with a siphon too often. Stationary inverts, like sponges and clams, need a good balance of light and water flow to access nutrients. You need to do your research or ask your veterinarian or local pet store owner for advice.

How many invertebrates should you keep in your tank?

When you add fish to your tank, it's important to limit their numbers to avoid excessive waste that could disrupt your water quality. But with invertebrates, you don't have the same concern, as they actually help reduce waste by scavenging and consuming algae.

Instead, when it comes to invertebrates, many hobbyists recommend simply making sure there's plenty of space for everyone to move around freely. If you have an especially small tank, such as five gallons or so in size, you might only want a few invertebrates at the most.

Some invertebrates are a little pickier when it comes to tank size, so keep these special situations in mind:

• Snails: Since they feed on algae, having too many will cause them to run out of algae and starve. Start with just a small number and see how the algae levels hold up.

• Hermit crabs: If there are too many in your tank, they may fight, damage your corals, or even pull your snails from their shells. Start with just a few and watch how they behave.

Research Each Individual Species

In addition to these basics, individual invertebrate species can have their own unique needs. When adding any new species to your tank, you want to understand its unique dietary needs, lighting, and water flow requirements.

Knowledge is power when it comes to being a saltwater aquarium owner. With research and care, you can have a diverse, healthy tank full of beautiful invertebrates that will delight you every day.