So I took John's advice and got a gallon bottle of Metricide. It turns out the Metricide 28 that I got is actually less strong than the Metricide 14:
Metricide 14 - 2.6% Glutareldehyde
Metricide 28 - 2.5% Glutareldehyde
It's still a hell of a lot cheaper than Flourish Excel which is less...