[jenhuei]

Flourite Black Sand? If so, it's ultimately going to get mixed in with the Amazonia over time. Which won't really be a problem - just be prepared. And Amazonia won't break down as quickly as you think it will.

The lower intake on the Flex is there to prevent filter burnout if you allow the water level to drop below the upper intake, so you shouldn't have a problem. You could seal it up entirely if you wanted. Just be sure to do top-offs so you still have water flow into the filter compartment.

Thanks for your insight. However giving the chance since i have not flooded the tank i m thinking to dig up some soil at the back and put up a barrier between the soil n vent (a mesh with rock perhaps) to allow water to flow. I am also concern about dead zone if solely rely on the upper intake.

 

[jenhuei]

There is a similar intake vent on my old fluval spec v. I routinely covered it up when scaping and never had an issue. /shrug it's your tank and you can do whatever you want with it, but you don't have to change anything for your tank to run normally.

That is reassuring. In that case i will keep it as it is. Thanks for the feedback.