Both of those products get rid of ick once you've seen it on your fish. Don't use medication as a preventative measure, especially that stuff. It's actually bad for the fish. It just happens to be worse for the ich.
My suggestion would be to continue to treat the fish for the COMPLETE DURATION SHOWN ON THE MEDS. This is vital, as the part of the ich life cycle you can see (the white dots) is actually impervious to the meds. Only several days later do the meds get to do their thing on the vulnerable phase of the ich. I repeat, do not stop medicating just because the white spots go away.
Read
this if you want to learn more about ich. There is plenty of information out there on the internet as well.
Here is just one of many pages that discuss ich prevention and cure.
As far as prevention, there is nothing more important for preventing ich than keeping all your parameters good (ammonia 0, nitrites 0, nitrate <20) and your water clean. Making sure your fish aren't stressing one another with aggressive behavior is another important factor.
Adding more fish (along with all the diseases they may carry with them) directly into the tank is another great way to cause another outbreak of ich, or something worse. I wouldn't add another fish until:
a) all of the ich is gone and stays gone for 2 weeks
b) all parameters are good
AND
c) an additional 2 weeks pass with no new illness or water problems
You would also be well served to get a small (10g) hospital/quarantine tank to keep newcomers in for several weeks until you know they are healthy. If you can't do that, ask the LFS to hold your fish purchases for a week.
Hope this advice helps... (it would have helped me a few weeks back...)
Good luck!