For a tank that size you definitely have a few options you could look into... Im going to guess you want something slightly more active, so maybe you could try and see if any of these puffers are available:
Carinotetraodon salivator (Striped Red Eye Puffer)
Monotrete Abei (Abei Puffer)
C.Loreti (Red Eye Puffer) can maybe do 3F / 1M mix
C.Irrubessco (Red Eye Puffer) can maybe do 3F / 1M mix
M.Turgidus (brown puffer)
All of these remain quite small but will work for life in a 70G quite happily...
P.S. Im no puffer god...just another puffer enthusiast
Carinotetraodon salivator (Striped Red Eye Puffer)
Monotrete Abei (Abei Puffer)
C.Loreti (Red Eye Puffer) can maybe do 3F / 1M mix
C.Irrubessco (Red Eye Puffer) can maybe do 3F / 1M mix
M.Turgidus (brown puffer)
All of these remain quite small but will work for life in a 70G quite happily...
P.S. Im no puffer god...just another puffer enthusiast
