Hi everyone. So I've been having a hard time keeping up with evaporation. My SG is constantly on the rise, and continues unchecked. I'm too busy to deal with adding water every single day, which is about how often it needs to be done. Long story short - my constant fluctuation has caused the death of my hammer coral. Anyway, I decided to build an ATO. I wanted something simple, fail safe, and quick to build. I didn't want to purchase a $100 unit online and have to wait for it to come in. I didn't want to use any valves / switches that could stick and cause a problem, so I based my build on a siphon method my LFS guy suggested. I googled it, and didn't find a whole lot, but the idea is simple, so I headed to home depot to see what I could come up with. I'm sure many of you are familiar with siphon driven ATO's but for those like me, who aren't, here is a breakdown. The idea is simple: An airtight container rests higher than the sump. The container holds RO/DI water, and has two lines going to it; one to the base of the container (to allow water to drain from it, to the sump), and one line to the top of the container (to allow air in, for water to flow out). Line one (connected to the top of the container) is a breather. This line travels from the top of the container, into your sump. You fix the end of the line in your sump at a desired water level. As long as the sump maintains the full level of water, the end of this line is submerged, and will not allow air to move into the RO/DI airtight reservoir. Once the water in your tank evaporates to such an extent that the water level in your sump drops below the end of the air line, it will allow air to move back through the tubing, and into the top of the RO/DI container. This allows water to move through line two, which is at the bottom on the container. The water will flow through line two, into the sump, until the level rises and occludes line one, stopping the movement of air, and causing a vacuum that will hinder any further flow of water. Provided your container is airtight, and your lines are secured correctly, this system is pretty fail safe. IMG_1656 by Brett Marillier, on Flickr IMG_1658 by Brett Marillier, on Flickr IMG_1659 by Brett Marillier, on Flickr IMG_1661 by Brett Marillier, on Flickr I have tested the system, and it is working great so far. AIR TIGHT is KEY! Feel free to throw any questions / suggestions my way. DIY = Manly!