Nah, you can skim the surface to remove it.
tanks utilize some type of overflow system. Since these overflows ingest the water from the surface of the tank, it's usually not seen. Since you're using a canister filter, this will be an ongoing thing. It happens in my FW
One thing you can do to help is take a powerhead and aim it towards the surface of the water. This will help to break the slime up so that it doesn't stay on the surface, so hopefully the canister filter can collect it and filter it out.