Mini-refugium/sump

Tank size: 100 gallon freshwater.

Sump size: 10 gallon (for now.)

Intake feeds at a maximum of 700 GPH and return pump max is 525 GPH. Average recirculation is 350-450gph @4ft head height.

Spraybar 1/2" X 3-1/2 ft, Holes= 9/64th dia 1" apart.

Substrate: 5lbs black gravel

Filter media 1 layer of 3/4" blue/white, 2 layers of lowloft batting
Bio Media: 1" bio-balls
Final filter: Bio-degradable "Eco-snow" poly batting (very fine and very soft.)

Not at all. There are 4 inches of bio-balls why do you need more, that is far more bio-surface than any HOB has.