Disease fungus etc problems

[mcvancleave]

Ok got this problem. I wet to a local pet store ad bought some fish that infected my tak with ich. Now it seems i stay with some type of problem. Even after treating for the ich it comes back along with white mouth or some other problem.
What i am looking for is some idea on how to stop this is a UV light a good way to go or is it not going to work. Is there aother way.
I do my water changes weekly.

Tank Info:
55 gal Tank
Wet dry filter 300 gal pump
Submersable Power Head
Took off protein skimmer figured waste of time
Added aqua tech 30 (added yesterday)
Using filter media and activated carbon
Fish Left:
3 Mollies
3 Guppies
1 Angel

[OrionGirl]

Frequent water changes are your best defense against disease. Most disease problems arise only when water quality drops, and frequent medicating can compromise your bio-filter, further impairing water quality.

You may have some problems with the combination you have--the guppies and mollies prefer hard water, while the angels need soft water. Mollies are prone to a variety of health issues when kept in soft water.

For future purchases, I strongly suggest setting up a quarantine.