I've never read anything about testing for chlorine resistance. Chlorine is more like fire than poison to plants, so it would depend on many things. There would be a lot in gravel for chlorine to react with and once it reacts it's gone. Unlike something like copper which kills a cell and then the copper is released to go kill another cell. People put chlorinated water on plants all the time, but of course pools can have a much higher level. But it's the same type of deal, can a plant heal from the damage. So fast growers would always have a better chance imo. A bigger and older plant would have a better chance imo. But that also means lots of roots. More roots mean the plant could lose a bunch of roots to chlorine and still recover. I wouldn't worry too much. My guess is any plant would do fine. Easy enough to try some.

Hi Charle 7 - I, have a gardening friend and we help each other out in the garden. So, here is what we did with her pond to clean it up. We drained it first, to be able to see the plant roots as it was a jungle of tangled masses- just as you mentioned. As we drained it down, then we could see all the growth. We had to get in the pond and pull the heavy plants up and we used large knives to cut the plants apart. That was the only way to get at the plants, they were sooooo heavy with all the roots!!!!! It took us three hours, to get her pond in great shape. If you can, ask a friend or two for help. You will need it, as plants grow and multiply so fast in a pond. If , you get to clean out your pond - I would love some of the plants. Let me know ,if you would like to trade! Good luck, tina

There is a dwarf water iris but I do not know if plants of it are available. But you might want to consider various species of Acorus. Check locally or at native plant nurseries online.

It IS a violet, Viola species. Would need to see the blossoms to get much more specific than that - there's several that are native to your area and that prefer moist soils.