Takes even less effort to top off your tank with fresh water compared to changing actual saltwater but most would agree a standard ATO is a must have these days. Not only to make your life easier but to promote stability. AWC is a very simple concept with a programmable controller with salinity measurement and employing a such a system is just another way to promote stability and free your time for more important things like actually enjoying your tank. If you enjoy manually mixing and changing water that's cool but most would agree it can sometimes be a hassle and often gets neglected.

water changes
 

What I have set at this point is very simple. I have 2- 30 Gallon drums (coke sells used drums for about $20). One is filled with fresh water and is connected to a float switch in my sump. The other tank has saltwater in it. I use one water lifting pump for the top off and 2 pumps for the water change. The water change pumps turn on and off together throughout the day. The problem is that the 2 pumps must have the same flow rate. I checked them and they are almost the same. I also have a second float switch that turns all the pumps off if something stays on or off. It is not a perfect system but it seems to work.:idea:

Yeap a very common method and works well for many people. With almost any system you'll still need to check salinity and make adjustments. Even systems with conductivity probes I still found the calibration/set points required slight adjustment every few weeks.

Rather than matching two pumps I find the use of float switches to remove and replace a consistent amount of water takes a lot of the guess work out.

Would a double stage cylinder be a better choice if it could be produced inexpensively?what volume would you need to move?

The chemist in me really really cringed at this. Saturating the salt water mix is bad idea.
This would work IF we were only using one salt, but the mix is just that, a mix. All the different chemicals that make up our fairly expensive salt do not saturate at the same levels.
This saturation is used sometimes to purify (removed unwanted salts) in many production chemicals. The NaCl would be almost the highest solubility. So you end up with just mostly NaCl and almost all the calcium and trace minerals would be what would precipitate out of solution.


Think of it this way -- if you dumped a whole lot of salt mix and pushed it to saturation, separated the precipitate out, add more salt mix and repeat -- you would have some expensive NaCl without much else in it.

So how would you make a good solution that could be handled ?

This is a real question, I respect your expertise, what would be a better method?

Sorry for the delay in responding -- been away a few days again :)

If you want to get really, really particular you could look up the solubility of each "ingredient" in the mix, and from the ration in the mix figure out how dense you could go.
Off the top of my head, I would be that it would be the calcium. as it is already super saturated in NSW anyways (magnesium is what allows this). As you start pushing the salinity to 2 or 3 times the normal amount, you could expect to see calcium precipitate out onto pump, glass, and everything in the super saturated hold tank. It will also push the equilibrium of the carbonate and probably cause issues with the buffering ("chalk" precipitate)

If you have a calcium reactor, or some cheap way of replacing the calcium you should be OK as most of the stuff in there does have a high solubility. Just always expect your salt mix to be very low in calcium and add as needed. If you are buying the super expensive salt with NSW levels of calcium, they you are wasting a lot of cash. IO salt is typically low on calcium and low in magnesium as well.

The best way, would be to not over saturate your salt as I'm not sure what else would go a little out of whack.

I'm almost thinking that the easiest and best way of doing this, is to just mix up a ridiculous amount of salt water at a time and do the "2 balanced pumps" to handle the water change -- mostly because I do add magnesium, some buffer, and calcium to get my cheap salt up to par and this might be easier with a larger volume of water. IE: 200 gal salt water storage in the basement and just change a few gal a day.
I don't think the salinity could get to out, and with a controller, you could just add some salt water instead of fresh to raise, or pump out a bit and add fresh to lower the salinity...... This way, you wouldn't really care what the salinity in the storage tank was (high or low) and let the controller work it out for you.

Yes this was my original concern with the method as well. However as mentioned I tested it long term on a reef tank with good success. I did not experience any precipitate and the levels in the display remained as consistent as the previous method of manually mixing and changing water.

When you think about it, it's no better or worse than how water is traditionally changed. Most people don't mix a full bucket of salt at once to insure optimal levels. Instead they grab a few scopes here and there which can result in different levels each time.

Not sure what you mean, can you explain? There is of course is a ton of different methods to remove and replace a consistent amount of water, I just mentioned one that I've used before.