I think the enamel needs to be changed
I don’t know how to whiten a bath 
I doubt if it’s enamel, baths now are normally made out of fibreglass.
A good bath cleaner would bring it back to life.
Yes, i remember when they moved in, they put some blue bath cleaner on it and let it work for a long time and was clean as new after
Bleach is the best cure for it 
(I’d advise you to wear rubber gloves when doing it)
Mix ½ cup bleach into about a gallon of water. Using a sponge, coat the tub’s surface with the bleach and water solution and wait 5 minutes. After 5 minutes, scrub the surface with the sponge, paying special attention to the tougher stains. Rinse the tub with cold water, being careful not to splash the bleach.
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Bleach is not a good idea for fibreglass, better to use a good bath/fibreglass cleaner for best results.Just my view for what it’s worth
Can I use bleach on fiberglass tub?
Bleach is safe on fiberglass or white porcelain. Mix ½ cup bleach into about a gallon of water. Using a sponge, coat the tub’s surface with the bleach and water solution and wait 5 minutes. After 5 minutes, scrub the surface with the sponge, paying special attention to the tougher stains.
It’s amazing what you find on the internet 
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Another gem you can find on the internet as well 
…
Generally, bleaching a fiberglass tub can cause it to become damaged. Bleach is a harsh chemical that can cause discoloration, weaken adhesives, and generally break down the integrity of the surface of a fiberglass tub.
If it is applied in a concentrated form, it can etch the surface of the tub or react with additives or colors that are part of the material of the tub, making the surface appear stained, pitted, or otherwise discolored.
Furthermore, bleach can break down grout and sealants used to protect the surface of the tub, and can even seep into porous materials such as grout and caulk, leading to gaps and water leaks later on.
It is best to avoid using bleach on fiberglass tubs or, if it must be used, to dilute it as much as possible and remove it as quickly as possible after it has been applied.
It’s just as well it’s a plastic one then
I’m not sure everything is amazing that you can find on the internet 
unlucky for me I found you eh 
you know I’m joking love you really 
it’s ok i have stopped blushing now pal
Couldn’t agree more pal
Probably having a team meeting on how to clean the bath without using a product that may cause the bath to implode.
Check your settings, especially under Widget Replacement. Don’t know if that will help, but it might be worth a try.
Do you know why they’ve been offline for so long?
Possibly that the apartment is having a deep clean or the plumber is in to replace the bathroom furniture.
Don’t ask