I don't use the entire intake tubes on these filters, only half of them so I forget if the bottom section is slotted/has holes. I used the aqua clear 70 filter foam inserts on 2 of them- make hole in middle (lengthwise) about 1/2 way down sponge & slide over the intake tube. You then can trim/adjust sponge to see what works best for you. Less material over bottom, stronger flow- more material, less flow. The other I used black filter foam for a canister, wrapped over the bottom & secured with a cable tie (like wrapper on lollipop).