I breed cories and use old fashioned box filters or corner filters. In the filters PEA GRAVEL and hypoallergenic pillow floss. [much cheaper than filter floss and the same get it at your local craft or textils shop.]I keep the tops of so the floss is eay to get at. Like McLendon says cories like to stick there eggs in or on something. I use java moss and fern broadleaf plants. If they lay on these I pull them if all over the glass I pull the fish other times they will lay in the filter pull the floss. When I puul the eggs I use 1 tank per week to put eggs in. I use sponge filters here less fry damage greater o2 amounts generated for good egg developement.