Thank bro
Previously I used RO water but it was too much hassle. For small coral tank I'll go for ro but large fowlr tank I won't go for ro. My sump tank is rather small, 3ft x 2.5ft which was a freshwater tank previously. Has a skimmer octo 150c, uv light (auto on 12hrs per day, media, coral chip etc.
I kept eel before but when you want to catch it out when it's eating your fish, you will surely cry or remove all your live rock out of it and cry the **** out of your lung. Just bear in mind, any fish you want to keep also can, but they must be compatible with each other (etc some angel fish single gene per fish) and you won't want to try catching them if you want to. 6ft tank is a large tank for catching fish. Till now I still have a couple of fish I need to release but couldn't catch it. I'll guide you how to catch it in future if you ever need to. Hahaha
From experience, for some particular beautiful angel fish which you most probably will keep if you are playing fowlr, take note some are really territorial like koran angel. Once you keep them in the early stage, any other similar looking fish like butterfly or smaller angel, coral beauty, will surely be chased around and stress till death. So release those territorial fish lastly (well for me it was always my last one which I swear to my wife when BUYING THE NEXT FISH HAHAHA) or can try to change the rock scape everytime you put in a aggressive and territorial fish so they will be busy findng new spots. But really very time wasting by changing rock scape everytime you place a new fish. I've been doing these all along so from experience it's not fun at all LOL
Hope these helps after 10 years of keep fowlr tank