You'll need to do two things:
1) Keep the tank cycled with some living creature or recycle with biospira when you add the puffer and
2) Slowly increase the SG if your keeping the tank cycled so you don't kill off the good bacteria.
I'd first see what SG your LFS keeps the puffer at (was this a GSP which will need a larger tank later or are you going with a Figure 8 who'll love that tank forever?). Anyway, many brackish puffs are kept in FW or FW with aquarium salt, so you'll need to use marine mix slowly for both the puffer and your bacteria. Increases of .001 SG to .002 SG per week are safe.
Eric
1) Keep the tank cycled with some living creature or recycle with biospira when you add the puffer and
2) Slowly increase the SG if your keeping the tank cycled so you don't kill off the good bacteria.
I'd first see what SG your LFS keeps the puffer at (was this a GSP which will need a larger tank later or are you going with a Figure 8 who'll love that tank forever?). Anyway, many brackish puffs are kept in FW or FW with aquarium salt, so you'll need to use marine mix slowly for both the puffer and your bacteria. Increases of .001 SG to .002 SG per week are safe.
Eric