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Try 50/50 bleach and water with baking soda...Use a throw-a-way spray bottle. When you use chemicals I assume you you goggles and rubber gloves. Your best long term bet is to remove and replace grout and make sure it is real clean before applying new grout of choice.

Clean the area well and make sure the area is dry. Use a tub and shower caulk, allow the caulk to dry for at least 2-4 hours before you shower again. It sounds like you had used the wrong type of caulk or didn't allow the caulk to cure proper. Good Luck

if it is black that is more than likely mold or mildew. try using a bleach pen. or a mold and mildew cleaner....

You coul also try using a toothbrush for the first cleaning so that when you scrub it .. it gets really clean.

Good luck.

buy some outdoor clorox and wear gloves and a face proctor on

put in a small spray bottle and squirt the discolored spot

Sounds like mold. Use a scrub brush and Soft Scrub with Bleach.

Clorox bleach

Water is probably getting behind the chalk causing the mold. You should remove it and replace it. It's relatively easy to do.

i have the same problem where i live and the landlords won't fix anything so i tried using comet cleaning powder and i used an old toothbrush. it works really well.

good luck.

I use the spray cleaners that have bleach. It really works fast!

best to remove it and re-caulk. try latex, as silicone is overrated.