I don't think there is an exact amount... Just fill as many fit in the sump, just make sure they are submerged 100%.
I plan to have bioballs/scrubbies under the drip tray and ceramic rings on the bottom.
I would stick w/the scrubbies u have n add Cersmic Rings as both deliver in different ways
Just my 2cents
My question is... "What's the best way to clean New Ceramic Rings?"
I have been told a few different ways n it kind of starttled me
I have done close to the same with other media but was thrown off with some replies of "boil in hot water because..." "rinse then let sit in the sun for a week", "rinse with bleach" and "wash in hot water then cold water right after..."
These verbal answers threw me for a loop. My plan was to rinse them real good with a garden hose like I would with new sand.