It really varies. I have one retic that went from 2.5' to 10' in one yr!! The other 3 are growing MUCH slower. I have went with the idea of preparing adult size enclosures for all of them from the get go; just because I never know what the future holds in terms of time ect... I have placed dividers in some of the really big tanks to consolidate since the retics are still small which makes 4 easier cleaning--I still have several big tanks in storage.
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steve