There is no definitive answer to this question as it depends on a number of factors, including the type of fish you are keeping, the size of your tank, and your personal preferences. That said, some filters that are often recommended for slow-moving fish include canister filters and hang-on-back (HOB) filters. Canister filters are typically more powerful than HOB filters and can better handle larger tanks, while HOB filters are usually easier to set up and maintain. Ultimately, the best filter for slow-moving fish is one that will provide adequate filtration for your particular setup while also being easy to use and maintain.