you want to rise the salnity slowly if you have the puffer in fresh water there is really no math to it at all you just need your hydrometer and id start over with new water to do it and id start your little guys out at a salanity of about 1.010 to1.012 and raise it gradually to 1.016 allmy brackish fish are here are completely heathly this including 1 green spotted puffer 2 figure 8 puffers 2 moray eels and 3 Columbian sharks but you will need a protein skimmer it is a must I suggest the one made by instant ocean for up to 100 gallon fish tank its what I have and it rocks but the most important things is to have fn with it and be patient with it