I am not familiar with those filters or what a water depurifier filter is. Is it meant for a fish tank?
The 55G has your juveniles...you are not going to have fry in there correct? So no need for the covering to save fry?
General info that may help you. You need to know the GPH of your filters, and your tanks should be between 8X and 10X GPH.
In a fry tank you can use a sponge pre-filter over the intake to keep fry out...or mesh covering the intake could work as long as it will not rot in the water (cotton) and not get sucked into the filter itself.