6' rusty galvanized stock tank

6' in diameter, 2" in depth. 390 gallons. Tarter brand stock tank made in Kentucky, US. We got this at the start of the pandemic and it served as all those years as a plunge pool. Because we used chlorine, it eventually damaged the zinc plating and the tank developed a rust problem. We've tried many things to clean it and coat it, but it's of no use against chlorine. But it would work really well as a giant planter. Or even a pond (if you use a pond pump and filter with it). Using a rubber spray against the existing rust might stop it from rusting further. Just avoid chlorine.