I never used a filter for the larva tanks, just large tanks (120 liter) and after transition to frozen foods a skimmer.
A filter just removes the live foods that you want the little guys to eat. And they don't make enough poo to justify a filter. Though you should remove leftover foods, poo and dead larva from the ground at least twice daily.
I only added a sponge filter cartridge to the power head pump that provided the flow after metamorphosis. And that sponge had to be cleaned daily.