OOOK once more Im in need of some help. I wasn't sure where to post this but since this will be a brackish set up I thought I would give it a try here.

My boyfriend recently went out and got me a trio of green spotted puffers. I have had my eye on them for a while. DAMN they are cute. So my LFS was having a sale on them so he went and got them for me.
YES i know they are brackish fish AND YES I know they shouldn't be kept in freshwater. BUT the guy at my LFS Swore up and down to my bf that they had been completely converted to freshwater and that they would be fine in my community freshwater tank. Everything I have read on the net suggests that they should be fine in freshwater for a while just not too long and that I SLOWLY introduce them to the salt.

I am now trying to set up my 20 gallon tank which I had waiting for these little guys all along but am COMPLETELY confused as to how to go about setting it up and cycling it ( I have already read the fishless cycling article but does this apply to brackish aswell ) also my API master test kit is for FRESHWATER is this ok to use with brackish water.

NOW what I have is
20 Gallon tank
Aqua clear 30
and a 15lb bag of instant ocean
and ammonia for cycling
THATS IT ... what else do I need for it?
also I'm using gravel from my 55gallon set up is this ok or do I need a different type of substrate like sand?
I really hope someone here can help me as I really wanna be able to keep these little guys ( I know they get bigger about 6" i have read) but for now they are my little guys.
Any and all advice is welcome .... PLEASE!

P.S. I have already started the cycling process "add and wait method" is there anything I should be doing differently

So your 20Gall tank will last a year or so, then you will need something about 4 times larger. (also are we talking 20 UK gallons or 20 US gallons as there is a huge difference between them)

As for setting the tank up, if the fish are in fresh just now, just clone the filter and be done with it. Once they are in the tank and settled (week or so) start raising the SG up by about .002 a week. until you get up to about 1.015 or there abouts.

sand will be fine for them or gravel as they dont bury them selves like some of the lurker Puffers.