White spot in brackish water

[Cara]

Hi, I'm hoping someone can help me!
I have just recently brought a "Topaz" Puffer fish. I was sold it as a freshwater puffer, but after researching the breed, I have found out that he is high-end brackish! I have now had him for a couple of weeks and he has white spot, I have been trying to change his water salinity to brackish conditions, and I also would like to treat him for whitespot, but with the treatment I have brought it says not to use in Marine tanks. Will I be safe to use in my brackish tank? According to my hydrometre the salinity is a 6 and the specific gravity at 1.004,I have only done 2 water changes so far to change the salinity, so it will be getting higher every week!
I hope someone can help as he looks really bad and I am so unsure what to do next!
Thanks
Cara

[Nick]

Generally speaking, the Ich will die as your SG goes up. One more water change should be enough to knock it out, actually.

[Cara]

Thanks very much for your advice, I have noticed since I did the first water change that he seems a bit more lively, although the whitespot seems to have got worse, he does seem "happier". His eye seemed to cloud over too, but that has now gone back to normal. I have just done my most resent water change this evening and I have been waiting 1 week between changes, should I be changing the water more often to get rid of the whitespot quicker? or would that harm him more?

[Nick]

You only want to change the SG by about .002 per week; extra water changes are generally not a bad thing, just keep the SG going up that amount per week to avoid killing too much bacteria in your biofilter.