Wooden deck in bathroom!

I have a situation in a bathroom where I need about 1 sqm of decking over a setdown beside a bath (long story, unusual bathroom!).

The decking will abutt marble floor tiles and any water on the decking will fall through into a drain below.

I was thinking of using merbau but am concerned about the tanin leaching and also mould. Tanin leaching onto the marble tiles would be a disaster.

So here are the questions:

1) Would merbau be suitable? I may be able to use silvertop ash instead?
2) Can I accelerate the leaching process (happy for it to be less red in colour anyway).
3) Should I then treat or protect the timber so it will not leach and not go mouldy?

Thanks in advance.

Virtually any new hardwood (regardless of its apparent colour) will leach tannins and even some old but re-sawn hardwood is susceptable. Sealing the timber in some way will help prevent leaching in the short to medium term however should the coating fracture or wear away then you might be back to square one...of course if you are careful then leaching may not be a problem for your marble.

Might I suggest a couple of alternatives? Is there any reason why this aesthetic set down (which I think I can picture) needs to be finished with timber at all?

One alternative is to use a plastic composite such as Modwood or even recycled plastic lumber (eg www.ausplaztik.com.au) which can be resurfaced with a vinyl finish woodgrain by yourself.

You could also cover the setdown with another material entirely - stone, steel plate, plywood, glass, acrylic etc or fill the setdown with gravel (covered by flagstones) or similar and let the water run through them....

G'day.
Use Red Mahogany for your "Duck boards".
Red Mahogany will not stain. Tha is why it was used to line wells in the old days.