You mentioned that you are on well water. What is the composition of the water pre-softened? Mine is high in iron and manganese. If yours is the same, you are going to have other problems to deal with, as in, your water will be brown and unappealing.
I too am on well water and I fill and top off my pond with water from after my water softener. It adds a level of salt into the water which is far below the levels that would kill plants, but there is enough to help keep your fish healthy. Added benefit, your water stays clear. the other day I received a bit of advice from another neighbor who owns a pond full of Koi saying to keep the salt level slightly higher than normal. It'll keep the fish healthy. When I asked her about plants, she said that if the plants can't tolerate the salt, then they don't belong in her pond. She has loads of cattails and grasses and lily pads.
Also, if you don't have good cover over your pond, the algae will bloom and turn your pond green. I've used algaecides in the past but they are temporary fixes. This spring I put a UV filter in line between my pump and waterfall and the water, which was pea green, turned crystal clear in a matter of about four days.