There are hundreds of chemical out there claiming that they are the best tub cleaning product. Which one has you already tried and think that it's the best?
what are you trying to do? what type of tub you talking about? Acrylic? ceramic? coated plastic?
Most general cleaning: Vim with bleach works wonders. If it comes already severely stained and not even full-strength bleach can take it out, i'm afraid that your top coating on your acrylic or gel surface is damaged. The only way to restore that is to go look for those 1-day tub restoration services, which they will prime and then re-coat a fresh new coat of acrylic onto your old, worn tub. Good for a few more years of service (the coating will eventually wear off, back to your old, tired/stained looking tub). Your other option is to take the measurement and go shop for a brand-new one,and coordinate with reno guy to rip apart the old one and install a fresh new one. Good for at least a decade or more.
I tried to use CLR to clean the peach color stains & green color stains on both the acrylic tub & gel coat shower.
A gentle brush, the peach color stains went off easily. Then I brush real hard for a long time and it looks like the green stains are still there. I have a soft brush which won't scratch the surface coating. Now I am seeking for the strongest chemical for cleaning.
I like Amway's cleaning products. Although more expensive but worth the money coz you only use a little bit at a time. I like LOC in particular. It's not abrasive (no gloves needed) yet, cleans wine, pen, crayons, grease very well! You can even use it as dish detergent.