I have done a ton of research on this but haven't been able to figure out how much dwell time is too much. I stumbled upon a couple of great deals, a Penn plax 700 canister for $50 and an 18 watt coralife turbo twist for $60. The turbo twist recommends min 200 max 400 gph but the penn plax is rated at 185gph so will be lower with media. Would that much dwell time have negative effects on the water? Or would it actually be more effective...any educated answers would be appreciated!