It depends on how often you trim plants, replant and live stock, I clean mine monthly~~max 2 months.... with 50%~70% water change weekly. Tho' you feel like its not need to clean, but actually there is...for flow rate and if you are using inline reactor its get clog.
@Ryu1~~No wonder why you have those nasty Algae in your plants....Clean often. 1 year is a way way to long to wait to clean..
haha, no I dont think so, i believe it is because of my light being too strong, beside those are new filters in my high tech. The one that i didnt clean for over a yr is a low tech algae free, maybe i am just lazy. I still think cleaning it every 6 months is adequate.