Starting a new tank!

I have kept a 55 gallon freshwater tank for some time with a pair of Columbian Sharks. They are reaching about 8 inches and I have decided I needed to upgrade the tank and start to convert them to brackish water, and eventually full marine. I have read that I need to add about .002 more salt every month til I get it to a brackish water (want it at 1.012)... give them time to reach full maturity, which I was thinking when they are a good 12-14 inches... and then I'd start to up it to a marine salinity (would like to see it at a 1.024). I have a 72 gallon bowfront I will be starting this out in.

Has anyone tried this and could possibly give me a few pointers?

The 72 gallon is predrilled and I will be running the sump and was wondering how I could use that for a filter while it's being converted from the freshwater to the brackish. I was thinking of just using the bio-filter from the 55 gallon, but I was interested in other methods (such as using the sump).

Any info is much appreciated! Thanks in advance!

Thanks for the reply!

I was thinking the same thing for the 72 being too small when they reach their full size... What I want to do is use this 72 gallon to convert them to the Brackish water and get the tank established... once they are ready to be switched to a marine tank I'd like to have a 200+ gallon for them to live in and I will have my 72 set up to where I can add some GSP's and a few BW gobies....

I would like the full marine tank to be mainly just for these guys. I haven't quite decided if, or what other fish I'd like to have in there if I decide to add anything more, maybe a few gobies (I love these guys!)...

Let me know of any other suggestions!

Yeah, I realized after I posted it here that I probably should have posted this first in the Brackish discussion thread. (which I did do... but you have been the only one to respond as of yet).

These sharks are actually in freshwater when young... and travel out to sea throughout thier life and end up in the ocean by adulthood from what I've read (thus having to convert them from fresh, to brackish, and to marine). It'll definately be something quite interesting to do! I hope I can get this all to work and have them stay as happy and healthy as they have been!