Water change system idea and ideas wanted

[MMM33732]

So I've been thinking of an idea of how to set things up so a water change would only take 3 min to do and use no extra pumps to do it.

Basically it involves adding an extra tank that is used for the change and also allows you to measure exactly how much water is being changed as well as adding some filter floss to the overflow water (plus increase the total system volume). So heres the quick paint sketch:


The tank size would depend on how much water you plan to change on regular bases. So say you have a 150g system and you want to change 10%, then you would want 15g changed, so I would use a 20g tank because the entire thing will not be full of water since the display overflow and filter would take up room. Now I suppose you could do away with the entire filter and have the overflow coming straight in from the top if you wanted, but I like the added filtration and polishing which would always be removed later down the road.

The sketch is pretty much self explanatory... you have a valve on your RO/DI tank to drain it into the saltwater tank. In that tank you would have added the salt earlier to have it all mixed already so you would be all ready to change out with aged water. You'd pretty much just have to turn off the return pump from your sump, open the water change tank's drain valve and drain it all out to whatever level you measured off. Then, close that drain valve and open the saltwater tank's valve and let that fill up the water change tank until you are right back to where water is overflowing into the sump again. Thats it... well them make some new saltwater.

I think its a pretty good idea since it uses only gravity to do the entire thing. The only pump would be an optional powerhead to keep the saltwater constantly mixing if you wanted.

So what do you think? Anyone have any other water change ideas that allow you to measure exactly what you take out and put back in? I'd love to see them. Any ideas of ways to maybe improve my idea?