Not sure how I feel about hanging this sump to your tank, especially since your DIY. There's a PVC connection on the side of that, if anything maybe have a drain from your tank via a PVC pipe to that sump, if that connection can be used. If done correctly I feel it could be a nice complete setup with the UV sterilizer. When you setup the sump and before completely filling it with water, you'll have to turn off your pumps, let the water drain into the sump with no power, mark that line. Just keep adding a little more water till you get to where you want in your sump, maybe an inch or so down. That will be your max fill line, that way you know if the power gets cut, the tank will only drain to that level in the sump. When you turn the pumps back on the water will go back into your tank and you'll know the water fill level in your sump, you can get a float attachment for this or simply mark it, whatever works for you. Also I'd check the specs on those pond pumps, some of them are not made for salt water, they might work for a little bit but eventually might send slight shocks in the water, you'll feel it if you put your hand in and its not good for your fish, the last thing you want to do is kill your fish trying to save money on a pump.