Parasitic worms? HELP

2 weeks ago, I was cleaning Jaspers tank, doing a partial water change & changing filters {there are 3 filters in his tank} & saw very small worm/leach looking things. I was pretty freaked out, needless to say. So, I did a serious cleaning, not that his tank was filthy, but I was grossed out & concerned.Here I am tonight, getting ready to give him his nightly snack & SOB, I see some of those things at the bottom of the tank where the gravel had been moved about!UGH!! I’ll have nightmares for sure! I disinfected my hands & then checked here in previous postings to see about parasites/worms… and saw something about food & cheap “meal” fillers. So I checked his Zoo Med “natural” pellets & saw all kinds of plant fillers… soy, wheat, etc..So, can crap food = worms?Then it dawned on me as I was taking pics to show with this posting that many of the rocks I have in his tank {large & small} are ones I have collected from beaches/deserts, etc… and although they were clean {again, I thought they were clean}, it made sense to me that these could be the problem.Jazzie does not appear to have these nasty things on him & his appetite is still strong {He has grown by leaps & bounds since I first got him in January}, but I find it hard to think that this is not a serious issue.Any and all suggestions/comments will be greatly appreciated!!