My guess is that the odor is from the decaying matter in your HOB filter combined with not running a skimmer. The yellow color could be either bacteria or algae. Either way, I wouldn't expect carbon or purigen to be of much help.
What would?
The UV light should help but they can only do so much. If the bulb is bad, it can make algae problems worse. You could try an algaecide like Vibrant if you wanted, but I don't think it would be worth it. In my opinion, the best thing you can do is keep your filters much cleaner and regular water changes.
Great! Keep in mind that the UV lamp is only an aid that is masking the impact of less then ideal husbandry practices. You should still work on cleaning your filters much more regularly.
A white slime could be indicative of Brooklynella. There is some reason to believe that antibiotics like Kanaplex and Bi-Furan can eradicate it but I would keep a close eye on them for awhile, along with any new additions.
With Brook, it is excess mucus that is stimulated by the parasite and sloughs off. Still, I wouldn't worry about it too much if the symptoms cleared up. Just keep an eye out for it in the future.
