I've seen that before when someone overdoses that product. You can reduce it in the tank with water changes, but that doesn't necessarily solve the problem of chemical concentration in the fish's tissues or damage already done to them, which would be factors why your fish are still doing badly after a water change. Not familiar with the chemicals in that product, whether there's something that will neutralize it, etc, but I'd think the best shot would be to get it completely out of the water and hope this helps the fish eliminate it better.
For green water, UV also works well, that and/or pothos and/or pleco much preferred to chemicals imo. Or, at worst, from what I've seen copper based algae products are probably safer than that stuff. Still doesn't address the cause, though, if the tank is overfed, gravel needs cleaning, lot of phosphate in your water, or those sorts of things.