I have a similar setup and haven't had many issues, I have a 47g column tank and a Rena xp4 canister, and I've only lost 2 fish, one jumped out (diamond goby) and another was kinda sickly after acclimation and was harrassed by other tank mates(domino damsels) and died it was 1 of 2 fire gobys, the other larger healthier goby is still fine, I did give the damsels to a friend after that though. This is my first salt tank, it's about 6 months old. I do have a skimmer now but didnt always have one, and I'm on my second, my first was a pos sea clone, that I fully modded and made it tolerable, but not good, I now have a eshopps ps 75, and it's much better than the sea clone but not perfect.
With the Rena I have switched out the biological media ( I had bioballs and stony type bio media) with live rock rubble. I also have filter floss and some DIY carbon and filter pads. I feed flakes once a day. And frozen cubes or shrimp 1-2 times a week. I have a pair of snowflake clowns, a fire goby, a purple fire goby, a 6 line wrasse, and a mandarin (just got purple goby and mandarin + 1000 pods). I have acropora, montipora, goniopora, Xenia, zoas, Kenya tree, maxima clam, frog spawn, a condy nem, a feather duster worm, mushrooms, a few other small things, I have 2 pom pom crabs, a porcelain crab, a sea urchin, 3 turbo snails, 7 hermit crabs, misc worms and pods, 40-50lbs of live rock and 40lbs of sand.
I've lost a couple coral frags mostly because of the turbo snails knocking them around and me not being able to get them easily or quickly.