Just wanted to post my Semi/Automatic water changer system I installed for my 600 gallon tank. Actually it just involves turning on the faucet. This has worked for me for the past year. May not work for everyone elses set up but it works for me.
1. First I turn the AUTOMATIC TIMER to the water volume I want. I do 100/150 Gallons every day (Mon-Fri). Since the process is more diluting than changing, by doing every day withing the 5th day it's changed about 50%. This will shut off automatically once the timer is done.
2. Then the water passes the triple filter. 1st is a prefilter, 2nd and 3rd is a Carbon Filter.
Planning ion adding three more cannisters =-)
3. Then it's up the PVC Pipe into the Fishroom. From there it's plumbed through the wall and into the tank. The flow of water is on the upper RIGHT hand side of the tank.
4. As the water fills inside the tank and the water level increases. It drains down the 3 bulkheads leading to the 125 sump. The bulkheads are located at the LEFT side of the tank.
5. The output from tank to the sump is directed to 2 Filter Socks.
6. As the water level rises in the sump it drains from the 2" bulkhead I drilled on the RIGHT hand side of the SUMP.
7. As the water drains from the sump it's directed to the outside of the Fishroom and into my garden.
This system works for me because all I have to do is turn the faucet on and leave. Even if I forget to turn it off, it will shut off once it fills to the desired amount. Also because my tank is pretty big in volume adding 100/150 gallons of water without heating it doesn't change the water temperature drastically where it affects the fish. Just wanted to share cause I'm pretty proud of it since I put it all togheter myself =-)
It looks great man! 
