So first of all... I didn't come up with this. Credit goes to scolley from RC. It is super easy though. So... I wanted a automated daily water change. I read an article by Randy Farley about the subject. The myth goes that big water changes are better than multiple samll ones. While that is technically true, the degree is very small. On my 100g system, I want to change out 30% monthly...30g. Crunching the numbers of 1 gallon a day comes out to be the effectiveness of doing a monthly water change of 26g. I cna live by that. Second.... doing automated water changes is a little tricky. You don't want to activate a ATO if you have one. Using two different pumps requires them to be matched. Dual head peristaltic pumps and dual diaphram pumps are often used but are pretty pricey. So I wanted to use a second Tunze Osmolator to do saltwater change...just turn off one and turn on the other.... but while researching I found the solution and it is brilliant. I already had a Osmolater and a controller. All you need is a second osmolator pump... $25.... and a relay... $20. I all ready had a spare osmolator pump and controller so this was a no brainer. So... all you need is to use a DPDT relay. You turn the relay on and it switches control of the Osmolator unit to the salt water pump. You then use a pump to get rid of some water, and the salt water osmolator pump makes up the difference. Here it is laid out. Two pumps, a relay box and a Osmolator. Here is the relay wired up. All you need is a project box from radio shack, a 120v DPDT relay, and some connectors. The whole thing cost me $18!!! Here it is all set up. So my Controller turns on the relay and now the Tunze ATO uses the salt water pump for top off. I turn on my waste water pump for 80 secondes to pump one gallon into the waste jug in back. After the Tunze tops off with salt water, I turn the relay off and go back to topping off with RO/DI water. Brilliant. I can even power the relay when doing drip aclimation or using water to dip new corals and top off with salt water. The waste jug has to be done in such a way to prevent siphons. And I'm not worried about overfilling jugs cause it is only a gallon a day and I have a 7 gallon jug, so I can just change out jugs as needed or just turn it off if I'm out of water. So far I love it. The whole thing cost me $18 for the relay box. An extra Tunze pump is $25. Extra hose is $10, but I had enough hose from the first Osmolator to have enough. You have to get extra hose from Tunze cause it is special size. You also need a small pump to get rid of water, but I had a MJ 900 laying around so that was covered. And you need a controller, but my Apex covered that. If you are on the fence about a Osmolator... which is an awesome ATO.... with a few exra parts, you can also automate your water changes. Just keep in mind though that the Osmolator will only run for 10 minutes and then shut down if it does not make level (emplty water jug) so you can't change out so much at one time to go over that. But even at that... one daily change would still be 70-80g a month so that is still a big tank.