Well there are different ways to do that, I'm presuming it's a hang on the back filter (
HOB) so we'll start there. Kitchen sponges are fine as far as I know as long as there is nothing added to them and they're new. You can wrap it around the intake tube to keep him from getting sucked towards it and that will also slow the flow down, you can also place sponge in-between the lip of the filter output and the lid to slow it down further, or cut a water bottle in half in the mid section and fasten it on to baffle it to the sides
fluval also makes what they call prefilters that fit over most intakes so you could look into that, most fish stores should carry that or something similar. You can also use dried out sea sponge as a sponge if you want, I've used that before because I had some on hand. Also, there fabric on filter inserts is sold in thicker pieces on lengths of it that can be used to accomplish the same thing. So you have a lot of options here! Hope I answered your question
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