I'm going with the zeovit suggestion for zeolites of 100gph per 100g of tank (115g tank and using a 100gph powerhead which is slowed down some because it's lifting water into the reactor which is 24" tall).
I'm not sure there's a hard and fast science to it though. My recommendation is "not too slow and not too fast."
Yeah I know that's not very definitive but that really is sort of how I approach it though!
Hope this helps.