The best replacement for bio balls is ceramic rings.

The best alternatives to bio balls are rated as following:
★★★★★  ceramic rings
★★★★★  live rock
★★★★  refugium
★★  ceramic media
★★  lava rock
★★  biomax
★★  ceramic noodles
★  filter sock
★  lava rocks
★  no bio balls
★  live rock rubble
  bio wheel
  bio bale

Your alternative for bio balls is not listed? Suggest!
Speaking about bio balls, one probably shouldn't forget about live rock.

Other search terms related to bio balls and their ratings are:
★★★★★ live rock
★★★ refugium
★★★ reef tank
You have in mind a companion for bio balls and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of bio balls in all years. Click on graph for more.
bio balls
ceramic rings
live rock