Hardest Saltwater Fish to Keep

Hard-to-Keep Saltwater Fish and Smarter Alternatives for Your Reef Tank

Before we jump in, we’re not talking about the rare, expert-only fish that almost never show up for sale. This list sticks to fish you’ll actually see at your local fish store or online, the ones that are easy to buy but not always easy to keep.

Some saltwater fish look incredible at the store, but once they hit your tank, things don’t always go as planned. The challenge isn’t just keeping them alive. It’s getting them to actually thrive long term.

A lot of these fish come from environments that are very different from a typical reef tank. Temperature, diet, shipping stress, and competition for food all play a role. The good news is there’s almost always a better option that gives you a similar look or personality without the constant struggle.

Here are some of the most commonly challenging saltwater fish and what to know before adding them to your tank.

Blue Spot Jawfish

Why It’s Difficult

Blue spot jawfish are often kept in tropical reef tanks, but they actually come from cooler waters. That mismatch can lead to ongoing stress and a shorter lifespan. They also need a deep sand bed to feel secure and build burrows.

What to Consider

• Naturally from cooler water environments
• Needs a deep sand bed
• Often struggles long term in warm reef tanks

Better Alternative

Yellowhead jawfish are a much better fit for reef tanks. They come from tropical waters and adapt far more easily while still giving you that same fun burrowing behavior.

Fu Manchu Lionfish

Why It’s Difficult

These guys look awesome, but getting them to eat is where things fall apart. Many won’t accept frozen food and rely on live feeding, which isn’t realistic for most hobbyists long term.

What to Consider

• Often refuse frozen or prepared foods
• Require live food to survive
• Hard to transition onto a stable diet

Better Alternative

Dwarf fuzzy lionfish are way more forgiving. Most will take frozen food quickly and are much easier to keep fed and healthy.

Boxfish

Why It’s Difficult

Boxfish don’t handle stress well at all. If they get stressed, they can release toxins that harm themselves and everything else in the tank. On top of that, they’re slow swimmers and can’t compete well for food.

What to Consider

• Can release toxins under stress
• Poor shippers and easily stressed
• Struggle to compete during feeding

Better Alternative

Dwarf puffers bring a ton of personality without the same level of risk. They’re more durable and easier to feed, though you’ll still want to watch them around corals and inverts.

Butterflyfish

Why They’re Difficult

A lot of butterfly fish are built to eat coral in the wild. Even if you get one eating prepared foods, there’s a good chance it’ll still pick at your corals.

What to Consider

• Many species are natural coral eaters
• Sensitive to shipping and acclimation
• Feeding can be inconsistent

Better Approach

If you’re set on a butterfly, you’ll need to be very selective about the species and where it’s sourced. Otherwise, there are plenty of reef-safe fish that give you great movement without the risk.

Deepwater Dwarf Angelfish

Why They’re Difficult

These fish come from deep, low-light environments with cooler temperatures. Replicating that in a home aquarium is tough, and they don’t always adapt well.

What to Consider

• Used to low light and cooler water
• Very shy and reclusive
• Specialized diet that’s hard to match

Better Approach

Unless you’re building a very specific setup, these are best left to advanced hobbyists.

Leopard Wrasses

Why They’re Difficult

The biggest hurdle isn’t long-term care. It’s getting a healthy one and helping it adjust. They don’t ship well and often take time to sync with your tank’s light and feeding schedule.

What to Consider

• Needs an established tank with natural food sources
• Sensitive during acclimation
• Requires sand for sleeping and security

Pro Tip

Feed when the fish is active, not just on your usual schedule. That flexibility early on can make all the difference.

Small Anthias Species

Why They’re Difficult

Small anthias have extremely high metabolisms and need to eat multiple times a day. Miss a few feedings and they can go downhill fast.

What to Consider

• Require frequent daily feedings
• Need very small food particles
• Thrive in high flow environments

Better Alternative

Larger anthias species tend to be much easier to manage and don’t require quite the same level of feeding intensity.

Banggai Cardinalfish

Why They Can Be Difficult

You might be surprised to see this on on the list as they’re often labeled as beginner fish. But the reality is, they don’t do well in high-flow tanks. In SPS systems especially, they can struggle to find calm areas and end up stressed.

What to Consider

• Prefer lower flow environments
• Smaller individuals are more sensitive
• Can struggle in high-energy reef tanks

Better Alternative

Pajama cardinalfish are usually more adaptable and handle a wider range of conditions.

Key Takeaways for Choosing the Right Fish

• Match the fish to your tank, not the other way around
• Look at where the fish comes from and how it lives in the wild
• Be honest about feeding and care requirements
• Choose fish that are known to adapt well to captivity

At the end of the day, success in this hobby comes down to setting yourself up for it. The right fish makes everything easier, more stable, and a lot more enjoyable.