RO water on a FW tank (unless very specific stock) is highly overkill. Treat tapwater with Prime etc and your just fine. For example CRS (Crystal Red Shrimp) which are highly inbred require very specific water so stock like that RO will work best.

What FW stuff did you want to throw in the tank?

I'd think for you a 50gal/day RO system would be just fine.

Plan on 55 gallon SW
And a depending on what size I get
Atleast a 150+ for a fire eel. Wanted a sting ray too but not sure if there compatible.

Not sure if they would work out together...my reading says that eel by itself.

I cannot comment too much on that stock but to give FW forum a good look see. I'll pm you a nice FW forum.

The thing you need to remember in an apartment depending on size and age the water may be traveling through miles of copper pipe. I have no idea if this matters but I would run ro at minimum. Just my .05 (no 2 cents anymore lol)

But will any filter fit in any ro/di system????

you cant tell me that a filter will fit in all the ro/di units on the market....

it would take ages to figure out which filters fit right in which systems... I would bet when you buy a system you are stuck with their filters.

I agree, Calgary water is some of the better water. I have even done big water changes by just using tap water with some prime.

I run RO/DI 4- stage I bought from BRS. Work well. We have a drinking one but I decided to go with one dedicated to the tank. I actually use it with a connection right to my tap as opposed to hard wiring it - that may work for your apartment if you don't want a more permanent install. The BRS one I got had an adapter and then I just went to Home Depot to get the right adapter.

Since all salt mixes were designed to to use at least RO water(some High forehead made it that way)I wouldn't risk it.When Calgary starts to put aluminum in the water come spring run off you may want to keep that in mind.If you're downstream from any high populace you're dealing with everybody's medications they're peeing out(still want to drink the water?)If you want to Know what's in Calgary water go to the city waterworks website and check it out.