Caulk the seam.

Which ever you do, caulk, grout or both, keep a microfiber cloth in the shower area and wipe down after use - each and every time. I got in that habit years ago and always kept an extra washcloth in the shower just for that purpose. Now I use the microfiber cloths from Costco - something like $15 for 36 - and my shower is dried after each use.

Scrape it out, put bleach in the space with a small brush to kill any remaining yuck that you cannot scrape out. Let it all dry, then caulk.

-Babka

Scrape it out, put bleach in the space with a small brush to kill any remaining yuck that you cannot scrape out. Let it all dry, then caulk.

-Babka

Use 100% silicone, not latex, caulk.

Thanks all!

We have DAP Kwik Seal for kitchen and bath--is this appropriate to use?

Bleach apparently won't kill mold (read this somewhere while researching/cleaning). When we had a recurrence of tile/caulk darkening in one small spot at the base of the MB tub surround, I scraped out the caulk in that spot, and then hit the space with vinegar, hydrogen peroxide with and without baking soda, not necessarily in that order. After cleaning it all off/out, I let it air dry really well, and then re-caulked, using the same siliconized latex caulk (that matched the grout). If it does happen again, we'll scrape out the caulk, and use 100% silicone caulk.

We also wipe down the walls with a microfiber cloth after showering, especially where the tile meets the tub. I couldn't find a squeegee that I liked, and I think the cloth does a better job wiping away water droplets (which, with our moderately hard water, leaves ugly water spots on our shiny white tile), and does a better job sopping up the pool of water that would otherwise sit along the edge of the tub, at the base of the tile and caulk.

And may I say again, no question is dumb if you don't happen to know the answer. Dumb is saying, "Um, well, this may be right." and putting in a bunch of work that may be a mistake.
{{gwi:1473205}}

Bleach does kill mold, it just doesn't penetrate porous surfaces so it's best for non-porous surfaces like tile.

Thanks, suzannesl! ;) I used 100% vinegar for the deep cleaning but am open to going back with bleach or hydrogen peroxide if needed--looks clean on the surface but honestly who knows in the gap. We have a bunch of microfiber cloths so sounds like a good practice to adopt moving forward, too. Looks like DAP does make a 100% silicone caulk, but what we have isn't it, so maybe worth grabbing a tube of that instead. (The tube we have is 3+ years old anyway--I was pretty amazed it hadn't dried up in that time!)

Look for a good quality Silicone like a GE Silicone II or something matches your grout.

artemis78:

DAP Quick Seal is latex, not 100% silicone. I agree with millworkman.

artemis-
As cheap as I am, I would never use an old tube of caulk for such a critical application, even if it seemed ok. Spend $7-8 for a new tube of silicone caulk so you don't end up with a seam failure in the future. I don't know how wide or deep the joint is that you are trying to caulk, but it might need some backing so that the gap fills properly. If it is pretty deep, I might consider using a regular bathroom latex caulk to build it out to about 1/4" below the surface, and then do a final caulk after that has cured with the silicone. Finally, if you want a professional looking caulk line you might want to watch this 3 minute video...

Here is a link that might be useful: Perfect caulk line

Not a bad video, but caulk should be pushed, not pulled, in that application. Windex works just as well, but you need to wipe up the excess without touching your fresh bead.