Well it's been a couple of weeks since I've updated this thread. Not a whole lot has been happening with the tank. I'm still reading somewhere around 0.25ppm ammonia, this level hasn't changed in 2 or 3 weeks, I'm thinking about taking some water to an LFS for confirmation.
My other clown fish also died, he had something weird growing out of his head one evening, I was going to go into the City to get some medication the next day but he was dead by morning. Hopefully this isn't an omen of things to come.
I also tore down my rockwork today looking for that elusive mantis, but he was nowhere to be found. Lots of little crabs though

I'm starting to wonder if maybe whatever I saw all those weeks ago was either something else, or didn't make it through the cycle/starved? I do hear clicking and snapping from the tank every now an then, but I've come to realize that lots of things make clicking and snapping noises (ATO, heaters, light timers, splashes, etc.). I guess I'll find out when I add a CUC.