It doesn't look like a sump, looks like a hob filter with a skimmer built in?
No I don't sorry. Is it not working?
At the very least it's missing the motor for the skimmer. What does it do when you plug it in?
It looks like it hangs on the back if I'm not mistaken. It might not need an overflow. However I have never been a fan of bio balls on a salty tank.