Advice on Corten Steel water bowl

Hi ,I bought a corten steel water bowl about a year and half ago, the steel self seals when it has drainage but because the bowl is always full of water I dont think this process is happening as the water is getting alot of rust in it and fresh new steel is appearing at the bottom of the bowl.I even left the bowl on its side empty to allow the self seal  process to happen with rain for about six months but the bowl being filled with water seems to still negate this process.

Does anyone have experience with corten steel water bowls?

The picture is when the  rust has settled at the bottom of the bowl, it clouds up the water when disturbed.

I am looking for an appropiate sealer to seal the bowl that wil not be poisonous to birds once cured.The sealer needs to work when always underwater also.Any help would be great!