Why Do Starfish Disappear in an Aquarium

Starfish are sluggish creatures, so many aquarium owners don’t think anything is wrong if they don’t see their starfish for a few days.

They hide in rocks to feed and might linger there.

If you search for your starfish and can’t find it hiding in rocks or elsewhere in the tank, you might worry.

It might have disappeared due to acclimation shock, starvation, or water quality.

Why Do Starfish Disappear in an Aquarium?

When starfish die, they waste away in the water.

They will fall apart if you try to pick up a starfish mere hours after it dies.

Even if your tank’s environment is ideal for starfish, they might disappear for several different reasons. 

Acclimation Shock

Starfish are great to have in an aquarium because they consume uneaten food and algae. They are relatively low-maintenance once acclimated and help keep your tank clean.

Starfish are sensitive creatures, so you have to acclimate them to the tank. If you introduce your starfish to the aquarium too fast, the water can shock its system and cause it to waste away.

You should establish your tank with balanced water chemistry and proper salinity levels. Make sure the water is at the right temperature for the starfish.

Once you establish the aquarium, you can acclimate the starfish with the drip method or the cup method.

Drip Method to Add Starfish to Tank

For the drip method, let the starfish’s temporary container float in the tank. The tank’s water will level out the water in the starfish’s container over 10 or 15 minutes.

Then place the container next to the tank. Run a drip line, found at any aquarium store, from the tank to the temporary container. 

The flow rate should be two to four drops per second. This introduces new water to the starfish’s temporary container very slowly. 

Once the container is full, pour out half of it down the drain and allow more tank water to drip in. 

You’ll dump out half of the water and let it refill several times so the starfish can acclimate to the temperature and salinity. 

The whole process will take about two hours, but it’s important not to cut corners.

After you’ve acclimated your starfish in the temporary container for a few hours, you can put it in the tank. You should do this quickly to prevent too much air exposure.

Cup Method to Add Starfish to Tank

You should float the temporary container in the tank to even out the water temperatures for the cup method. As with the drip method, this takes 10 to 15 minutes.

Pour half a cup of tank water into the temporary container. Let it sit for five minutes, and then add another half cup. Do this until the container is full.

When the temporary container is full, use the cup to remove half of the water. Don’t put this water back into the tank; pour it down the drain, so the water’s levels aren’t affected.

When the temporary container is only half full, begin adding more water from the tank every five minutes as you did before. 

After you do this for several hours, you can remove the starfish from the container.

Since the container is already in the water, you can simply move the starfish onto a rock in the tank without exposing it to air.


If there is not enough debris and algae for starfish to eat, they will waste away as they starve to death. 

The tank needs to be large enough for the starfish to have access to a lot of food. They will eat any food that other fish pass by. You can also add coral to your tank for them to eat. 

However, it’s best to feed them live fish food like clams and mussels. This will ensure they won’t eat their organs and start to disappear.

While starfish eat other aquatic creatures, some fish will eat them. If your starfish was already unhealthy and wasting away, a creature that eats debris might consume the deteriorating body. 

Whether your starfish wastes away due to starvation or gets eaten, it may seem like the starfish disappeared to your eyes. In reality, it can get eaten by scavengers relatively quickly.

Water Quality

Starfish thrive in a tank that mimics their natural environment. Water that is too cold or has low salinity will cause a starfish to waste away. 

Keeping the water clean with a pump and filter system suited for the aquarium size will also ensure your starfish stays healthy.

This means your salinity level should stay between 1.022 and 1.025. Try to keep your water towards a higher salinity level because anything too low will kill the starfish.

Temperature is also crucial for your starfish’s health. The water should stay between 72 to 76 degrees Fahrenheit. 

Temperature changes have killed off starfish in the wild, and you don’t want it to happen in your home tank.

Different starfish species can handle various temperatures, so do your research to ensure your tank is a hospitable environment. 

For example, Asterina starfish adapt well and can survive in water as cold as 46 degrees Fahrenheit, but many others can’t.

Other levels of your aquarium water can influence the health of your sea star. Nitrite levels should never be above zero. This is toxic and will cause your starfish to disintegrate.

Calcium levels are also crucial for starfish. Coral in your tank absorbs calcium from the water, so you’ll have to add enough for the starfish to grow. 

Starfish use calcium to build and harden their shell-like parts. Without enough calcium, they will be more at risk of getting crushed or eaten by others. They can also waste away and disappear.

Adding calcium also impacts other aspects of the water, like alkalinity, pH, and hardness. 

When you add calcium, you have to make sure you’re adding enough to offset coral without throwing the other levels into dangerous territory.

You need to make sure that all other fish living in the same tank can handle these requirements. Some fish might not thrive at these temperatures or salinity levels.

Keeping Starfish Healthy

If you take proper care of your starfish, they can live for anywhere from five to 10 years.

Keep the tank clean and ensure the water quality is what the starfish would flourish in naturally.

Because starfish are predators in the wild, you should feed them similar foods in the tank. You can buy snails and live fish food at aquarium stores. 

If you don’t see your starfish when you check the tank, keep an eye on the rocks, sand, or other hiding places. Starfish often lie low and feed at the bottom of the tank.

If you notice that your starfish is disappearing, you can try to balance the water levels. Run a test and check the temperature and calcium, and salinity levels. 

If something is wrong with your water, don’t change it abruptly. The change will shock the starfish’s system and kill it. 

Instead, change the water levels as you did when you first acclimated the starfish. Use the drip or cup method to introduce new water over time.

Final Notes

Taking good care of your starfish keeps it from disappearing. Make sure you’re feeding it enough so it won’t starve.

Give it time to adapt to the aquarium water so it can thrive.

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