No the sump sits under the tank. The drain holes or overflow box are at the top of the main tank and once the water level has dropped below the point where it can flow out of the tank the drain is stopped, but your sump must be capable of holding this 3-4" of water plus the amount of water it usually runs with without spilling over should the pump stop. In your case a sump of around 200 litres (or there abouts) should be ample, you just need to work out the volume that 4" of height in your tank holds and then double it.
UV isnt essential but if power costs arent your main concern then they are a nice useful addition to prevent outbreaks of disease and free floating algae blooms, i dont use them any more because running several thousand gallons of water costs enough as it is without extra cost of luxury items
UV isnt essential but if power costs arent your main concern then they are a nice useful addition to prevent outbreaks of disease and free floating algae blooms, i dont use them any more because running several thousand gallons of water costs enough as it is without extra cost of luxury items
