If it were me is be just the same get a bucket and fill it with old tank water or treated tap. And let it soak for 5-10 hrs to make sure also after 5 hrs is up take rock out dump water and fill bucket back up with old tank water or treated and let it soak again then u would be 100% safe
Venustus get too big for that tank. I'd say they need a 125 when full grown. There's tons or mbuna that would work! Google mbuna profiles and go to the cichlid forum profiles page and look at what u like. Unless u have an awesome local shop for them ordering online is the way to go.
Hers a link. I can offer opinions on what u like. http://www.cichlid-forum.com/profile...gory.php?cat=2