raising salinity in an established FW tank

[SFeST]

Hear me out on this

I have an off-dimensioned glass tank somewhere in the ballpark of 40-50g with a fluval 304 that I want to setup as a quarantine for my current 100g reef. I used to keep an oscar in it for a while but he kicked the bucket recently. While I'm figuring out what to do with the tank I threw in a couple mollies to keep the tank cycled.

Question is now, what will happen if I slowly raise the salinity over the course of a few weeks or so? Will it kill off everything keeping the tank cycled, or will everything slowly adapt? I'm not worried about the mollies, I know they can take it. Good idea? Bad Idea? This to me is easier than taking the whole thing down, cleaning everything off, buying new media for the canister filter, then starting over. My goal is to have a nice quarantine constantly running and with fish in it to ensure its a nice environment, rather than setting one up/tearing it down as I need it. I'd be afraid that something might go wrong in the process one time.

I've been running a sponge filter in the sump of my 100g for a while now so I can hook that up to it to get things kickstarted if I need to start from scratch so it's not a big deal. Just wondering, in theory, what would happen if I add salt to it now.

 

[Sk8r]

unfortunately the two sets of bacteria aren't compatible: you're likely to get a frothing mess. If you raised it slowly over, say, a year, you might get something viable as a tank [though I'm not sure it would], but what you really need to do for your stated purpose is to totally ream it out. For a quarantine you shouldn't have anything but a plain floss/carbon filter and bare glass anyway. Your Fluval is ok, but ime there's little reason to have a cycled qt tank: use your discard water from your water changes to fill it, and if you're going to be using it for several rounds of fish, keep it up, otherwise dry it out and strip it down between uses.

 

[SFeST]

all I needed to know, thanks