New fish and sick fish

Question
Right now I have a 2.5g tank that I am keeping two guppies, one platy,
and one zebra danios until they get a bit bigger. I just recently put
the platy in and he keeps swimming up and down the glass. I also
haven't seen him eat yet but he seems very healthy and active. My water
balance(ph,nitrite, all that stuff) is how it should be. Do you think it is
some type of dominance display or something?

Also, (In my 15g tank) I recently had a gouramis who had threadworms
and before we could buy the medication he past on. We got the other four
fish, (2 australian rainbows, one gouramis, and a 1.5 inch algea eater)
out and cleaned the tank with hot water and boiled all the decorations
in hot water. Do you think they still have a chance of catching it?

Answer
Hi Tay,
With the 2.5 gallon tank and the platy, he is probably just seeing his reflection in the glass and wanting to follow that "other" fish. Actually platies really thrive best in large groups. Although I know this isn't possible in that small of a tank. You probably already had this in mind but upgrading to a larger tank would really be best for all those fish. And the platy may just need some time to get accustomed to the new environment before he will accept food. It's usually quite normal for new fish to not want to eat for a while as they get adjusted to their new home.

Now with the 15 gallon and the threadworms, you should not have any trouble with them anymore since you cleaned the tank so thoroughly. They should really be fine. Just keep an eye on them of course, you never know.

Best of luck and I hope this helps!
Karen~