Hi Sam
I am the person doug is talking about with the osmolator and kalk dispensor. It is the best thing I think I have bought for my tank for top off.The kalk dispensor would work very well in your tank.It is so easy to use all I have to do is fill my 5gal pail with water every 2 days and add 2 large spoon fulls of kalk.And the best thing is you do not have to worry about going away.Nobody can mess up or get confused on what to do.If you want to see pic's of it go to
www.reefaquariumguide.com and look in the members tank area under reefer mike.
Mike