That's actually a valid concern. Even with a fairly weak filter, an unwary or sleeping fish can get stuck or sucked in. Mesh over the filter inlet will fix that, but you have to clean it now and then.
Be sure to put plenty of plants in the tank, even if it's just a bunch of Java moss. It grows tiny buggies for the fish to eat, keeps the water cleaner, provides hiding places, and also looks pretty good.
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My current project, a 65 gallon aquarium stocked with vernal pool fauna.