If you don't want to use the overflow, you can always connect a ball valve or threaded plug (assuming the plumbing has a threaded female connector) on the outside end of the bulkhead fitting (where the drain hole is).
Though the sump is not necessary, there are benefits to using one. Along with providing additional volume and filter media to the system, a sump will allow you to place things such as heaters, thermometers, and CO2
reactors out of sight of the display tank.
If you choose to use the overflow and sump, you should take measures to minimize CO2
loss in case you are injecting CO2
. Not much you can do about the overflow and downspout. But in the body of the sump avoid the use of trickle media (bio balls, etc) ABOVE the water line. Sponges, IMO
are ideal over media with excessive void space when used above the water line. You can have bio media in the sump, just keep it submerged.
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