By ceiling fan, do you mean ventilation fan? How long do you let the bath fan run after you leave the shower? If this is on the ceiling, I wouldn't think it would be related to water getting behind the tiles from a normal shower. Is there something above like another bathroom that could be leaking? I would clean the whole shower including the ceiling to remove the spots, seal the grout since you are worried about that, and leave the bathroom vent fan running for 20 minutes after finishing showers. If that doesn't solve the problem, then you'd need to revisit it.

Try this! I discovered it purely by chance when we had contracters here who did the very same thing. I happened to have a "kleenex" (with aloe) in my purse on the counter, grabbed it, and the marks came right off. The next time it happened, I grabbed a paper towel. It worked, but not nearly as easily. I've tried it without the aloe-added tissues and it does not work. The aloe may just be the key! Let me know if it helps!

So what advice did your mold experts give you? Certainly not peroxide, baking soda & boric acid?? Have you heard of a product called Boracare? It is a mold inhibitor that sprays on & will keep mold in an inactive state. Understand that you can't kill mold, just keep it inactive. If Relative Humidity (RH) gets above 50% mold growth will be activated again. You can bleach it, kiltz it...but it is just covering the mold up for alimited time. I would first look for the moisture intrusion that caused the mold growth. Get a roofer with a good reputation & good flashing education to take a look at the flashing of the skylights. Is this where the moisture intrusion began? Also look at the wall covering in your bathroom. If you have vinyl wall paper this is a source of mold as it traps moisture behind it. Oil based paintd also make a vapor barrer on top of your walls. The paper backing on the back of sheetrock is an issue. There is a brand called Densearmor or Denseguard that has no paper backing.. For mold to grow it has to have moisture and a food source eliminate the moisture first and then determine if the food source needs replacing. Have an electrician hard wire the fan to come on when the light is turned on. Bath fans should run at least 20 minutes after shower/bath is finished to remove the additoinal humidity that has been introduced into the home. Best of luck to you.

Wedi is A great system . I have installed many wedi showers. Heres a few things I can share. If your tiler Installed all of Wedi Properly and used The *****PROPER WEDI brand sealant ON EVERY SEAM., the system is very solid. A wedi shower build mixed with porcelain or dense glazed ceramics and good grout will Dry out very fast after use, this means they dont retain much water if installed correctly. Things like the pan being set level, mortar selection and application, 98% coverage and proper key in. followed by pure silicone changes of plane and its pretty much a home run for me. If you called me to your home to investigate this problem, id first get a complete and detailed list of what CLEANING CHEMICALS you tried several of..... id politley advise you , you may have worsened or created this issue. :):):).... and how you applied them and removed them and mixed them. There is a reason we use Tile specific cleaners in showers and other than the Vinegar, Dawn, baking soda type remedies I dont veer to far outside of using ANY cleaners that aren't specific for the tile/stone and grout you have and I wouldnt be online taking random advise. I 'd call the MFG of wedi, or the Thinset/grout MFG, or the, Sealers/cleaners MFG Tech support. This is how the tile pros deal with these issues, direct from the horses mouth when problems arise. What I would be be looking at ( after what chemicals have been introduced) Id be asking for pictures of setting materials used to set all the tile, Id inquire about curing and dry times and focus on the possibilty you may have either latex leaching from a latex based caulk in the assembly, Or A Bucket ready mixed setting material in the vien of mastic or a new age grout not meant for submerged applications. Could be as simple as Using latex sanded grout caulk in the pan that will mold. Rest assured body and soap scum, in a properly built shower with the properly applied materials would have a real hard time producing this effect in a Wedi or topical waterproofed shower. . How is your bathroom ventilated? the fan runs after each shower? the windows get opened? etc etc..... Eliminate what chemicals you used that may be causing this and inquire about Grout, mortar, mortar coverage, Sealants at change of plane and the proper Wedi sealant was used. If your installer wont help you here id first call Wedi and request a site visit from there rep. My free advice to you based on My years of hands on Industry proven tiling experience and Wedi expertise.. -best