Lol, well your scenarios are a little different than most. Both tanks use dry rock/ sand and are pretty new. I suspect other unintended algae spores will be introduced with intended macro and corals. Over time a nutrient build up in the rock and sand may lead to unintended growth. It can be combated with skimming, gfo, WC, calcium binding, etc. but that made it sound like its a hands off process and I disagree.