I had an outdoors fountain basin that broke so I found a planter that I liked and I plugged up the drainage holes and stuck the water pump in. It holds but the water is really murky.

The planter is metal or fake metal finishing with an antiqued paint, I think. If this is rust or painting leeching into the water, I need to stop this from happening.

Is there anything that I can use to coat the inside of the planter to provide a water tight protective layer between the planter and the water?

I don't know if any birds will drink from this but if they do, I don't want them to end up with heavy metal poisoning, so that's another reason I need to have a protective layer on it.

Keeping that in mind, whatever I use to make a protective layer can't poison birds that may decide to drink out of it.

Thanks for any suggestions!