If you’re looking for how to get rid of sponges in your reef tank, you’ve come to the right place! While sponges can be beneficial to your tank and some aquarists attempt to add them to the tank, they have a habit of overgrowing coral and clogging up filtration systems down the road.
You’re not here for the pros and cons of sponges in your reef tank, though, so the best ways to get rid of them are to expose them to air, limit their food source, turn down the water flow, brighten the tank, introduce sea life that feeds on them, or use hydrogen peroxide.
Don’t Scrape Them Off
Before we get into the ways to take care of the sponge problems that plague your tank, it’s important to address the number one mistake that many people make: Manual removal. This is one of the worst things you can do!
Scraping sponges off of walls or rocks is temporary and might make your tank look better for a couple of days, but sponges are capable of growing from the smallest particle. By scraping the sponge into pieces, you’re actually spreading it and making the problem worse.
Sponges don’t respond well at all to air exposure, in fact it will dry them out and kill them. While your tank’s ecosystem might be used to a rock, you might be best removing that rock or whatever surface the sponges are growing on and letting it dry out.
It won’t take long, since even a second out of the water will allow air pockets to form in the sponge as the water drains out. You might even notice the sponge shrink a little when this happens. This is made even more effective for what it does to other sponges.
When you put a sponge back into the tank, the air bubbles that formed will prevent water from returning and kill the sponge. Upon death, the air bubbles will be released and affect nearby sponges in the tank, creating a chain reaction.
Starve Them Out
The good news with this one is that you don’t have to do anything different. Sponges need food to be smaller than half a micrometer in size, which is extremely small. Even the smallest food in a tank, like zooplankton or phytoplankton, is usually 4 times that size.
Sponges aren’t designed to survive in reef tanks, so they’ll eventually die out on their own if left to their own devices. Of course, you’re welcome to expedite that death.
The Flow is Too Low
On that note, this method of removal is especially effective in conjunction with limited food. Sponges need a higher flow of water to pull food to them, so if you can turn down the air current in your tank without hurting other life go ahead and do it.
This actually works in three ways because, on top of the feeding, water circulation draws waste away and prevents bacterial infections that can kill the sponges. To make matters worse for the sponge, though, lack of significant water flow can overwork them to death.
Collar cells in sponges rely on water flow to help shape and grow the sponge, so without proper water flow these cells are left to do it all alone. In many cases, this puts too much strain on the cells and that sponge will die.
Turn Up the Lights
A common misnomer is that better lighting will kill sponges when in reality it’s the situation that lighting creates. When your reef tank is well-lit, it will attract the growth of algae. Algae is generally harmless and is actually a food source for many organisms.
However, the other benefit of having algae in your tank is how it counteracts sponges. Algae will begin to gather on sponges until the sponge is overgrown with algae. When this happens, it can have negative effects on the sponge until it dies.
The overgrowth of algae will restrict water flow and prevent the sponge from feeding, both of which are surefire ways to kill the sponge if you recall earlier methods of removal. If your tank can handle it, go ahead and light things up.
Let Slip the Fish of War
The bad news is that most fish, especially ones that typically inhabit a reef tank, can’t or won’t eat sponges. Sponges simply lack nutritional value and don’t interest the majority of the fish. However, if your tank has the right conditions there are a number of sponge predators out there.
The number one feeder on sponges is the angelfish, whose diet is at least 70 percent sponges. The biggest drawback here is that angelfish will also completely destroy any coral in your tank, so it really depends on what else is in your tank and how badly you want the sponges gone.
There are a few other options, like triggerfish or filefish, but several of the angelfish will accomplish the task the best. Just do your research on which type might be compatible with the rest of your tank if any because they seriously will wreak havoc on coral.
While angelfish prey primarily on sponges, if they’re not ideal for your tank you do have options with some invertebrates. There are a number of nudibranchs, crabs, and snails that specifically eat sponges, so check if any of those would work.
Sea stars and pencil urchin are also known to feed on sponges, so you have a lot of options to add something to your population that’ll remove the sponge problem. Just be careful, because crabs sometimes eat coral as well.
If all else fails and nothing else works or is a viable option, you can use hydrogen peroxide to kill sponges without harming the rest of your tank. Especially with the filtration, simply dilute food-grade hydrogen peroxide down to around 30 or 40 percent concentration.
Once that’s done, inject 1 or 2 mL into the sponge, or multiple areas of the sponge if it’s big enough, and give it 24 hours. Hydrogen peroxide is usually highly-effective in killing sponges and none of these options will cause it to spread.
- Aquarium Invertebrates: A Look at the Sponges https://reefs.com/magazine/aquarium-invertebrates-a-look-at-the-sponges/