Tell the fiancee "love me, love my fish". I have seen many a swell romance go south over a lot less than a fish tank. Seriously, the photography (albeit of a mean ol' serpae tetra) in among those plants was beautiful. I think you and the fiancee need to talk about a fishroom for you!
BTW, the first fish I ever bought for my first ten gallon tank in 1970 were Serpaes. Never bought any since. . .