Fluval SPEC (not evo-freshwater version) filter conversion

[Nanolifeuk]

so I’ve had this tank over a year. Always struggled keeping coral and maintaining water quality.

it’s only 60L and exactly the same as the Fluval Evo except slightly taller + a filter grid at bottom (see pic)
I’ve noticed a surface biofilm problem despite good agitation, and my filter floss on intank media basket never gets very dirty.

Could this grid be stopping my overflow from surface skimming? I can see micro particles entering the bottom grid more than the top.

 

[Nanolifeuk]

I notice the main difference between these tanks is this grid at the bottom. Maybe if I glue an acrylic card over it, this may force the water to only enter the overflow