[NABRIL]

Hello
I have an outdoor gazebo that has 6x12 travertine pavers sitting atop a concrete slab. Two years ago, I had the floor of it cleaned and coated with a topical nano spray that was clear, and the floor looked amazing. Slowly but surely, the middle whitened. I will attach pictures. The perimeter of the floor gets wet from rain or from the well-irrigation water, so it looks amazing, but you will see that the middle looks horrible. The third picture is of a bit of water poured on the white area.
The company that came out to coat it 2 years ago told me that the humidity of the concrete slab will continue to seep up, and that the whitening will be periodic but constant.

What can I do to improve the look of the middle?

I'm thinking about cleaning the entire floor with some travertine friendly product (not bleach). After that, I would like seal or coat or do something to make it look good. I don't have any berries or fruity trees to worry about staining the floor.
1. What cleaner and sealer or coater do you recommend?
2. Is my plan a smart one?
Thank you

 

[Nealtw]

Not sure what the acid is that he is using.

 

[stadry]

probably hydrochloric ( muriatic ) - 8% is easily avail at apron/vest stores

 

[Druidia]

Any natural stone sealer and ENHANCER will darken your travertine tiles.

I have 17-YO travertine in our bathroom. I clean and reseal every few years. Some areas that get more activity tends to lighten/whiten more quickly. I spot seal/enhance just for the looks because I like my travertine tiles looking pretty