If you're worried about overflows in the sump you can always get a PVC check valve for your return line. This will prevent any back flows in the event of a power outage or just turning off the pump. Of course you can just measure how much water could siphon back into your sump and just make sure you have enough space in the sump to accomodate. BTW L"xW"xH"/231=gallons. I don't run a canister filter but I do use an Aquaclear filter with a sponge, carbon and Chemipur Elite in it. I wash out the sponge every week and it takes out a lot of particulates that the skimmer and LR don't take care of. I have no nitrates or any nuisance algae but I also have way too much live rock in the tank as well and have never missed a water change. A canister is more work to clean and if not cleaned very often nitrates can build up from the captured organic material as it is still in the water column until removed manually. Reactors may also be something to look at for carbon, etc.

I'd trust a properly sized sump and a return line positioned to minimize back flow or siphoning before a check valve that might not seat.

I do both, but I'm paranoid!

ive always found the best way to avoid an overflow is to avoid hob skimmers, coralife to be specific lol. Really though i avoided the sump thing for the first couple years but once i finally went for it my life got so much easier, less water fluctuation (chemistry, temperature). it also gets rid of some mess from constantly topping up the display tank. and if you want a more open display tank you can store liverock in the sump.

Paddy go with a sump it is so much better you have extra water volume and space to work with equipment. Build a large return chamber to deal with evaporation and if you want add a ATO. If you plan properly your sump won't overflow.

Sump:) Canister filters (IMO) are not very efficient for saltwater. A good wet/dry or sump is better and cheaper in the long run. Canisters have a slow flow rate and calcium deposits destroy the impellers as they are not really made for saltwater or they would make a salt and freshwater canister. For saltwater you would need better seals. Again just my opinion :)

Clearly everyone wants the OP to go sump :lol: however, i'm pretty sure OP has set their mind on a canister :)

Having said that, I do have some friends who use canisters and they seem to like their Eheims. I myself used to have one, a 2217 that was rock solid and lasted like 6 years until I sold it. What I really like about my Eheim was the fact that it had huge support. Everywhere I went someone sold Eheim parts for it.