Most fish take at least 2-4 years if not longer to reach full size but I still don’t agree with the thought of “planning” to get a larger tank in the future as a basis on choosing which & how many fish to keep. With the average cost of anywhere from $20 to $30+ dollars per
gal for a
fowlr or reef system having that 120+
gal tank is often out of reach for most aquarist for many years.
For beginner
SW aquarists the general rule of in/
gal in saltwater should be followed closely to alleviate fish stress/water quality issues
IMO and if you don’t have the space for your fish when they are adults then you are just asking for trouble down the road. Especially with predator fish which can be excessively messy.
Experienced fish keepers can exceed the rule slightly mostly because they often have the proper equipment for keeping the water quality high ie: 1+ lbs of
lr per
gal, quality skimmer, dedicated water changes with
ro\
di water, & frequent testing to ensure their results are working.