Yeah Physan20 is a nice alternative, one of few that is listed for viruses as well as a lot more.The only trick is an activated tea of some sort with aerocloners. Microbe tea that most RDWC guys use to keep the cyanobacteria at bay.
Bleach between uses does nothing, physan20 does more, also breaks down into nitrogen in 4 days and is more friendly with adding beneficials between cleanings. Bleach sticks to plastics too much.
i like coco if im going into coco. but i prefer oasis. holds the most oxygen.