Based on the info below it looks like the AC110 main difference is that it's a lot wider than the AC70.
AC70
GPH 300
MAXIMUM TANK SIZE 40 TO 70 GALLONS
WIDTH 6 IN. HEIGHT 8 IN. LENGTH 8.25 IN.
FILTER MODEL AQUA CLEAR 70 (OLD MODEL 300) MEDIA USED CARTRIDGES FILTRATION TYPE MECHANICAL, CHEMICAL, BIOLOGICAL
AC110
GPH 167-500
MAXIMUM TANK SIZE OVER 100 GALLONS
WIDTH 6.75 IN. HEIGHT 9 IN. LENGTH 13.5 IN.
FILTER MODEL AQUA CLEAR 110 (OLD MODEL 500) MEDIA USED CARTRIDGES FILTRATION TYPE MECHANICAL, CHEMICAL, BIOLOGICAL