I have seen green water from organically chelated iron -- that is, iron that was eroded from old iron or steel pipes by bacterial growth. These chelants (sideraphores) are apparently much stronger than anything you can buy commercially, and chlorine stable as well.

Your city is certainly old enough to have areas that will experience this problem, but you'd have to call your water company. You could also ask, in the same call, if they are adding anything to the water that would give it a greenish tint.

If you would, add another dose of bleach to both buckets. I'd assumed that the dose given was enough to break any chelant, but now I'm not so sure. I can't find anything on the oxidative destruction of sideraphores, and I don't understand the chemistry well enough to have any sort of educated intuition about it.

In the pool where I experienced this most notably, it would take up to 3 weeks for the greenish color of chelated iron to disappear.