maybe I need another 40 hermits or so...
I think my original problem stemmed from contaminated RO/DI water. I've solved that issue and my water is coming in clean, but I am unable to win the war that was started long ago.
I think flow is my current issue. I seem to have some dead spots. Another Vortech is on the way...overkill for a 75g, but I'll be upgrading in the coming months. With two Vortechs, though, flow should no longer be an issue.