What cleaning agents are best to get a bathtub as shiny and white as when it was new?

i used amonia with water let it sit for 5 mins and scub then rinse with viniger water. it works great.

Comet, comet, and then Iron Out. You'll be shocked at the results! Let the comet set in the tub for awhile before scrubbing, then rinse extremely well before you use the Iron out.

depends on what type of bath you have. I have steel and enamel and it sparkles with hot water and elbow grease. Acrylic or fibre glass baths scratch easily and take more care. A strong bleach maybe what's needed. I find Mr Muscle products work very well. Don't buy stores own brands or cheap brands as they aren't anything like as effective.

It'll never be shiny like new, that surface has worn off. But Zud or Barkeeper's friend will get out stains, it's oxalic acid.

There are a few things you can try, Soft scrub, Comet, Ajax or Bar keepers friend...

I use comet it keeps it nice & white as it cost 1 dollar.

you can use a soft scrub cleanser (liquid cleanser), and then used about 2 cups of bleach, just estimate it, mixed with warm water....this will eat away at soap scum like magic