[karimwassef]

I know I've shared this before, fast flow through a UV has no effect at all. It's a waste of the device and power. It would be like buying a 4000gph DC powerhead, running it at 5% and then complaining that the flow is so terribly weak and letting others know that it's a waste of money.

The impact is power x admittance x exposure time. Admittance is the cleanliness of your quartz sleeve. Power is a function of when you last cleaned your bulb and exposure rate is a function of geometry and an inverse function of flow rate.

One more variable is overall turnover. If you plumb the UV in a small loop that doesn't allow fresh (not yet radiated) water to be injected, the effect is lost.

Lights out pushes the dinos into the water column. I ran dark for days + slow flow UV.

If you're not removing the dead, you're just putting food for the dinos that haven't been zapped.

I apologize for being so pushy on this concept, but we use UV for industrial sterilization, food, hospitals, etc... The improper use of a device doesn't make it a bad tool. It is a remarkably effective tool if used properly.