20 Gallon Tall, Aquaclear 50 (being converted into a refugium) 2x Koralia Nano 425s, no sump, 20lbs sand, 15lbs live rock
1x yellow watchman goby
1x Red firefish
2x Ocellaris clownfish
would this be too much for a 20 gallon tall with weekly water changes?
The issue is behavior rather than bioload. Clownfish (of this species) once sexually mature will be aggressive and really want to control 25 gallons of tank space. As such the firefish will be intimidated. The watchman goby and (presumably) the alpheus randall shrimp should be fine. The firefish, probably not.