If they bubble when you pour vinegar on them it means some type of chemical has been used on or around them. You can wash well and try vinegar again to see if you got it completely clean. It's not very often that you'll find an "UN safe" rock. Most the rocks you find or buy from the hardware/garden store will be fine after a good wash.
There are several methods to cleaning aquarium decor whether you choose to bleach bathe, boil or just a real thorough rinse.
Just remember, fish come from the wild and are used to most of natures elements so don't be to hard on yourself. Steer clear of metals and chemicals and you should be fine.
I have pea gravel in my aquarium that came from home depots garden section, pots from their garden section, and rocks and wood that I've found at parks and by a near by creek. I boiled some and bleach bathed some and all my fish are fine.
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