You have to find the source of the water before filling it back in. Otherwise, just more mold in the future. Is there no foundation below the tub? looks like it's all dirt, not just around the drain.

Thanks for the response! There is foundation. That’s the drain pit. It’s a lot larger than it probably needs to be. Maybe 2ftx1ft, so not the whole length of the tub. I’m thinking when they installed the perimeter it created a crevice for water to leak in there. I don’t know. Hopefully they’ll fix it. Maybe I should fill the pit with gravel?

Don't know where you are located, but filling the pit with gravel wouldn't work with building codes in my area. What is supposed to drain into that?

You may get better advice posting on this site https://www.diychatroom.com/

It has more building/construction pros on it that Houzz does vs. decorating/design folks

Nothing is supposed to drain into the pit. The tub is supposed to drain into the pipe. Once we get the water issue taken care of, I’ll have to get a plumber in to replace the pipe maybe. This dirt area is much larger than it should be. I’ve read that you are supposed to fill with sand or gravel and then pour concrete on top, but obviously I’m clueless.

I’ll try diychat room thanks!

I understand now. Yes, that dirt area is waaaaaaay too big. The gravel should extend only about an inch or so from the drain and it's really for seepage around the drain that might occur from a tile floor (through the grout), not a place for water to pool. The seepage might occur because you can't get a watertight seal between the drain and mortar. when there is grout against the top of the drain. I don't think you should need this for a tub, but who knows. Maybe the drain was leaking. Hope you find a solution and ideas on diychatroom.

Thank you!

It’s a freaking nightmare! Ahhh! 😂