Flatworms are a pest that can be removed from the reef aquarium. There are several types of flatworms in the marine aquarium but they can all be killed or removed the same way. Some say some saltwater fish are known to eat flatworms but I have had no luck with fish getting rid of this pest and this includes trying several types of wrasses.
One type of flatworm lives on live coral like mushrooms, leathers, elegance corals and I’m sure many others. They can become so thick that if not taken care of that they will block the light to the coral and smoother it.
When they first start living on a coral, they can look like a coral with very small dark spots on it and then those spots just keep growing. These spots on the coral can also be a light white color to almost clear.
Then you have those rusty colored flatworms that plague the side of the aquarium.
If possible try and increase the flow in low flow areas where you see flatworms collect on the aquarium or live rock. Flatworms don’t like high water flow.
You should do a water change to bring the water quality up and the nutrients down in the aquarium. I have noticed that the rusty colored flatworms can be worse in aquariums with high nutrients.
With the flatworms that live on the coral, take the coral out of the aquarium and rinse it off in a bucket of saltwater. You can also rinse and dip the coral in salifert flatworm exit.
If you can’t get the corals out of the aquarium or the whole aquarium infested, then you can use Salifert Flatworm Exit on the whole reef aquarium. Flatworm Exit can be hard on some life in the aquarium like red worm rock and anything like that should be taken out before starting. Follow the directions for the Flat Worm exit closely and be cautious. I have had good results with Flatworm Exit but on occasion have had to dose the aquarium again a few days later to kill them all.