I am not totally sure how it works. Just make sure you get the candystripe(randall's) pistol, as Yashas and the banded high fin, pair with them exclusively in the wild, so your odds of pairing increase greatly.
On another note, regarding 5.5 gal tanks and AC70's, definitely get the 150 gph impeller for it, as the 300 is way too much if you have a sandbed. I switched and no more sand storm.