Though it’s a mild natural cleanser, vinegar will typically be potent enough to deal with most stains when applied heavily and given time to set up. Spray the tub down thoroughly, let the vinegar sit for a few minutes, then scrub away the stains using a sponge or stiff-bristled brush. If you discover that vinegar isn't having the desired effect, you can move on to more intensive methods. There will come a point when simply adding more and more vinegar won’t suffice. Products like Lysol All Purpose Cleaner, Kaboom, Shout! and Scrubbing Bubbles shower cleaner are good for eating away at tough stains without damaging delicate surfaces. Since most of these products contain a similar combination of ingredients, any of them will work as well as another. Just make sure whatever product you choose doesn’t contain bleach, as this can severely weaken the outer enamel layer of the tub.  Only buy cleaners that have been approved for use on enamel-coated bathroom surfaces. Be sure to check the label carefully before buying a particular cleaning product so you'll know you’re getting what you need. If possible, open a nearby window, open the door, and turn on a fan to ventilate the bathroom while you clean with any of these products. If you're reluctant to go shopping, you can formulate a simple all-purpose bathroom cleaner at home by mixing together warm water, baking soda, Castile soap and essential oils in a spray bottle. All of these ingredients are readily available and safe to use but are quite potent when brought together. Once they're combined, spray the mixture onto the stained surface and give it a few minutes to take effect before wiping it away.  If you're having trouble tracking down Castile soap, hydrogen peroxide will make an acceptable substitute. Essential oils like tea tree and peppermint can also act as natural disinfectants. Mist on the solution and give it a chance to sit. Pay special attention to places with heavy staining and discoloration. The cleaning solution should get to work dissolving these...

TL;DR in Indonesian:
Cobalah bersihkan bak dengan cuka terlebih dahulu. Gunakan semprotan pembersih bebas pemutih. Buatlah campuran pembersih alami sendiri. Basahi dan rendam daerah yang bernoda selama beberapa menit. Sikat noda dengan hati-hati.