Backabit,
For nearly sixty years I've used vinegar, and a little salt, on my cucumbers, salads, and holiday headcheese. Sometimes I use both on my fish and chips too. I always wash my hands with a good soap before I eat. But, I wouldn't ever think of using a commercial weed killer for any of these things.
I've also used strong vinegar, with a little detergent, to kill weeds in my walkways, the gravel edging around the house, and down the middle of my driveway. It works very well. Here too, I wouldn't ever use a commercial weed killer that could get on my pets or grand children.
It is a little hard to find, but I try to use 20% agricultural vinegar, cut with a little water. Farm supply stores frequently carry it. Being a moderately strong acid, it needs careful handling. When I can't find it, I try to use straight 8% pickling vinegar.
I've never added salt to my weed killer, but in the amounts you posted, I certainly wouldn't expect an issue on soil or around a pond. Based on the info we have about your pond, a cup of salt would be extremely difficult to even detect in over a million gallons of water.
I would have a concern about commercial weed killer, especially if you have lilies or other water plants you wish to keep. It wouldn't take much of a Roundup-type chemical slick to do serious damage. Yet, the salt and vinegar will mix with the water and disperse very quickly.
For the most part, I'd try weed whacking. Around my pond I mainly use either my weed whacker, or I back my bushhog over the edge for especially difficult growth.
Good luck, and keep us posted.
Ken
