What do u mean by a basic water fed system??
Depending on your system/brush you use;
Sometimes just good old water with some squirty (washup liquid) and a brush does a good job on its own. Ive done that for years.
Alternatively can squirt ciff on your brush after water the conny roof and scrub with that. Or use ubik2000 sprayed onto wet roof, leave for a couple of mins to break down the algae etc then scrub. Either way, plenty of rinsing.