ok I scanned through the zeovit forums and zeovit works just as great in a nano. The larger water changes are just fine. What has to be changed is the dosing frequency. Dosing less often. Basically about half as often.
I'm starting to get excited about this; It's gonna work
As for running it in a HOB filter, it's done often. Just have to knead it like kneading carbon. Or use a chopstick like christy said. The two little fishies reactor is overkill since it holds 3/4 L of zeovit, while I'd only need 1/4L.
Today is my 100% water change with RO/DI now that the rock's no longer leeching nitrates. I'll see if it's in stock at Gold's today and probably be running it very soon.