Here's an idea.

You should ask LMAT to put the things in their tileset that you're looking for! Sort of like a request line. As long as it's not too unreasonable (as in too difficult to pull off) or aberrant from the tileset theme, I'm sure they'd be happy to take your suggestions.

Also, in reference to the previous question about making a believable background, try making the Layer 8 fade color bright blue (disregarding my previous comment about green) behind the Layer 6-7 stuff. It may not completely solve your problem, but it'll enhance the mood.

Oh, and you should try using bubblers with differing speed settings under the water (the only place they'll work, btw). That could help.