We'e recommend the following:

1. For weekly cleaning: STONETECH®Revitalizer® Cleaner and Protector to clean weekly, STONETECH® Soap Scum Remover and STONETECH® Mold & Mildew Stain Remover as needed.

2. Regarding using baking soda/hydrogen peroxide to clean yellowing grout: Seems like a lot of work. This
mix could break down sealers depending on what sealer was used. If the
green/yellow is showing in certain areas we would be more inclined to think it could be some type of mold/mildew/algae that grows, which the STONETECH Mold and Mildew Remover will help strip.

3. Regarding yellowing of the grout: Without better pictures it is
difficult to say. The grout will not pick and choose where it will
yellow. If the 1500/1600 was going to yellow in an installation it would
do so throughout. Typically when there are problem areas it is due to
something else causing an issue such as mold/mildew etc… Also Marble has
iron and sometimes can rust and leach the color into the grout as well. We would not discount this from being part of the issue. We would recommend first trying the STONETECH®Revitalizer® Cleaner and Protector to see if this works.

If you have any other questions, please feel free to reach out to our Technical Services team at 1.800.243.4788 or via chat our on website: www.laticrete.com.

Thanks so much! I'll follow your instructions. Confirming that these cleaning solutions are safe for marble and I don't need to re-seal after each time right??

I wonder what's causing the discoloration. Do you know what setting material was used during installation of the product? Was it mastic? I have seen where mastic has caused white grout to discolor a yellowish green color behind glass tiles.

I have no idea but it doesn't happen to all the grout, just the one behind the sink, which makes me think it's actually molds/soap scum. We are very careful when using the sink to avoid splashes though, so I'm surprised for the yellowing to build up so quickly.

Does it flower out in a crystal form?

no. Literally it's just a bit of green/yellow color. and they come up with scrubbing and steamer. i'm guessing those are the spots from splashes when we use the sink?!

No telling, very baffling to me. This is just within the grout or also in the stone?

Here is a picture of very little greenish that has started to develop in the last few weeks. It's still very slight and shows very little in pictures but you can see the yellowing/greening in the grout corners next to the dark stone mosaic.

Interesting. Stone does carry iron and other mineral deposits and you might be seeing where moisture from the setting material has seeped into the stone affecting these deposits. This happens a lot with white stone counter tops and there are remedies that can be done to help remove them.
Read [THIS[(https://www.houzz.com/discussions/my-granite-is-turning-green-dsvw-vd~945605) thread. There may be something here that can help you remove the green.

Am I seeing the green spreading into the tiles themselves? I can see a roundish green bloom - the center of which is the darker tile. If I'm seeing this correctly, I would say this ISN'T the grout. I would say there is something else causing the green.

Things like COPPER will turn green as they oxidize. Iron turns "rust" red. I would bet there is a mineral either in the stone or behind the stone that is causing this. And yes....if this is leeching to the surface it is possible to clean away the green sitting on the surface. That may be why it goes away when you steam clean it.

Copper... for the life of me, I couldn't think last night.

It's hard to say because the 'green bloom' is very slight right now, sometimes i think it's just a reflection of the green in the grout...in the picture, the round bloom shows more, but in real life, the green in the grout bothers me more and I don't see the green blooms as much.

FYI, I used this sealer already, coated 4 times:https://www.amazon.com/Trewax-Indoor-Outdoor-Sealer-32-Ounce/dp/B000BYE9XY

Looks like I will use the stonetech products first and see what happens. Then I'll try the EZ off (but guessing I should use the lemon scented one because that would damage the marble)? Then I'll try the mangia macchia ....the tenax is not available right now.

The question is will all these products remove the sealer? Do I need to reseal again after I clean each time?

Nothing is ever easy...i am shocked to find out about the green bloom problem with granite. I had a white caesarstone installed recently and regretted it with all the scratches and problems, which I had gone with a light granite instead. But now it looks like white granite has problems too! Nothing is perfect I guess.

Also, as I mentioned, there are 3 spots like this behind the sink but no where else! This cover my entire wall floor to ceiling but the green spots only came up behind the sink. I wish it's elsewhere, where your eyes don't immediately go to it.

Yes they more than likely they will remove the sealer. And yes I would reseal the area once you have finished removing the green.