Treating Ich-should I change the water?

[Bling]

I've read as much as I can but I'm still not sure--- I'm pretty sure I have a case of ich in my 5 gal brackish tank (new) --- it's a case of wanting to raise some local fish, and I brought some of their water in, and gradually have been changing it, but I guess it's still got "wild" things in it --- anyway, should I change some, most, or ALL of their water every day when I add the medicine? I have "Ich Cure" (Formalin and Malachite Green) and the instructions just say: 2 drops per gallon until cured. How can you tell when the tomites are gone? Will the medicine just keep building as I add it? I'd like to put these tiny fish in a fresh, small tank with no gravel, but I'm afraid of stressing them further. Right now they're still lively and eating well. Thanks for your help!
(Temp. about 72 degrees, hydrometer reads about 1.003, nitrate test didn't show anything, but there's a lot of hair algae and plants I brought with them; don't have a test for nitrite; pH 7.4 or more)

 

[WILDER]

Have you done some tests on the water that you have fetched them in, if not do so, and also tell us your water stats from the tap in ph,nitrite,nitrate, do they look like they have been sprinkled in salt.

 

[Bling]

These fish are actually coming in from the ocean. They are fresh/brackish fish, but their first 3 months is spent as oceanic plankton. Then they find their way back to the stream. I took 3 little fish from the land-side pond, which was abosolutely freshwater, as far as my hydrometer said. (Previous readings have shown an average of 1.003, very high pH, and even though it looks filthy, no nitrate readings.) From the ocean-side I got 2 tiny fry. The water there was, where the fish were, was about 1.005. The water I took was from the fresh side. But when I saw the first spot, like salt, but a bit bigger, I changed some water, using a saltier mix. Also, got the medicine, but didn't use it. Then 2 the next day, the dot was gone. But this morning, there's more white spots on the others. It does look like salt, but kind of large grains. I've now added the medicine, but I'm wondering if it would be good to put them in a brand clean bowl or tank, with the next medicine dose. I'm afraid a buildup will kill them faster than the "white dots".

 

[WILDER]

You could do a water change, i wouldn't do a full one, maybe add abit of the old water they are in.
http/www.badmanstropicalfish.com/articles/article2.html