Shrimp! They just won't stop breeding!
I've had this tank for a few years. I started off with 4 shrimp, then 9, then we had a few tragedies and then down to 5, then 10, then 19, then 50, then 150, then 200, stable at that level for a while, and now - SHRIMPLOSION! No idea how many are in there, but it's close to a thousand.
We had a single ghost shrimp, and you can still see great-great-great-great-great-great-great-great-great-great-great-great grandpa's genes in there.
I haven't changed water in the tank for 2 years, just top-ups from evaporation. Very few deaths (though the dead ones get dispatched pretty quickly). Tank is heavily planted, including some house plants above.
I have to rescue a couple of dozen every now and then from the filter. Very happy with my invert tank (and the tetras/snails and ottos)