Ill never argue the fact that a sump would be the better choice. the answer should just be " your better off with going the sump route, but a canister will work if you choose to use one"
REASONS FOR SUMP -Additional volume, place for more rock, place to hide heaters, section for refugium, section for top off, section for reactors, THE LIST GOES ON..
I personally would go with a sump, I'm just saying a canister is fine for a marine system. Many people run them with great success and have been for years.
I bet you had great results changing your system but you cant compare you originally running just a canister VS changing your system and running a sump + refugium + reactors. Thats a totally different animal.
He could easily run his tank with the same equipment you have... The canister, hang on refugium, and a reactor on the tank and receive great results, hell he can run everything inside the canister if he wanted, filter floss,polishing pads, carbon, purigen phosphate pads...etc....
As for husbandry, It starts from the beginning. Strip all of the contents, use your own media, filter floss and/or pads and weekly maintenance. and making sure you rinse and replace media when needed.
all systems are different, i read some people running fx5's on 90 gallons and only doing monthly maintenance
When i read about canister users having problems its always a result of a poorly setup up canister or people leaving them be for too long thinking the waste disappears on its own. Almost always, when we hear about nitrate users on both sumps and canisters we immediately think or ask if they are running the bio rings or balls and instruct people to remove them.
Im not an expert on anything really, just read a bunch and check out a ton of systems on the net. Just wanted him to be clear that they would work if he wants too use one.