There no way of saying..as a general rule 4-6 weeks at least...my biocube only took about 5 days I used all live sand and rock..my 8g nano I never really saw a cycle..but I saw someones who took 4 months..So its hard to say..in both my tanks I cranked up the heat to about 85 because bacteria grows better in warmer water..also but a shrimp or two from the deli in there to kick things off.