Sponge Filter - Aquarium

Just started a brine shrimp tank to feed my tropicals and wanted a sponge filter that won't eat the babies or smaller shrimp so I decided to make a sponge filter that uses carbon wrapped in 2 layers of filter floss/cloth.

This should provide adequate mechanical and chemical filtering for a 10 gallon tank with 6 gallons of water.

I was thinking of trying my other design but it doesn't give any trapped shrimp an escape route in case they are caught.

But the question remains: Why design a