boomer,
I've given it some thought and I think I'll just add two more Pandas to my tank. I've had the Pristellas since 2012, but the Pandas are relatively new, just a few months old. They seem healthy and happy, although it's a bit harder to read them and I do worry about them from time to time.
I have to admit, the Pandas were an impulse buy - I was originally looking for dwarf corys, but I should have waited. I paid around 7 or 8 dollars for each of them, and the guy at the LFS warned me they can be tricky to keep alive. One of them did die the first night, but the rest have been doing fine.
Thanks again for your advice, and thanks to keyholder too. I'm feeling a lot better about my tank's bioload now.
Steven