Well if you want to rejuvenate your tigers, you might want to introduce some new tigers in there (six years of inbreeding can't do much for the species).
And then you could get something to coexist with them? Like Cherries, Yellows, Snowballs etc.
That's what I'd do.
First post here for what you want, and if not then search for Rare Aquatics on ebay.
Hope this helps!