Welcome Mike!
First off, I'd stop treating them wth the medication and change out part of your tank water ASAP to get it out of there. Puffers in general do NOT do well with medications, they have no scales and absorb things way too easily.
Are the white spots on the fins, and are they raised up like grains of salt? If so, yes, probably ich, and that can be treated with salt, fortunately for you, since you are going brackish anyways
If they are not raised up, and just on the body (not the fins) its just the puffer's spines.. they look like little white dots and most people don't even seen them until they look closely.
Definately check out our Library, there are a lot of articles to help you out, any questions, fire away and we'll do our best to help!
What were your nitrite readings? Nitrate looks good, but keep it as low as possible with lots of water changes.
and found this site. I have been reading some of these posts on your cool board and researching some topics and what not. I have two Gsp's in a 20 gal hex tank I know this is not large enough for them and plan on upgrading in the near future. I have put crushed coral and agronite on the bottome of the tank for substrate. and started to increase the SG of the tank. Also I noticed the puffers were kinda gray around the mouth and patially on the belly. What exactly does this mean? They also seem to have a slight case of ich. (small white dots on them) I have raised the temp to 80 degrees F and started treatment for the Ich. I am using a malachite green base soulution and have only given half the recomended dose. Should I stop treating them with this or give them their last treatment? I have tested the water parameters and they are as follows: Ph 7.7-8.0, KH 16, Co2 concentration 4.4mg/l, Nitrite No2 0.3mg/l. I ran out of amonia reagent But I keep up on water changes regularly. Eventually I would like to get them into a 75 gal or something around that size and setup some live rock. Any sugestions or info would be great! thanks all 
