I'm going with the ~200 gallon storage container. I'm looking at the LiterMeter III peristaltic dosing pumps for the Continuous Water Change. The pumps are calibrated by volume, rather than time so minor differences in pressure can be accomodated. The ATO runs independantly and has nothing to do with the water change system. It's an incredibly simple system.
However, the purpose of my post was to share my experience with salinity probes. They are increadibly sensative to stray voltages and tend to wander all over the place. Curt at Apex recommends that the salinity probe be placed in a drip cup to completely issolate it from the sytem. I was never able to get a consistant reading from my probe and basically threw it out.
Another concern is the mixing rate of new saltwater coming in with tank water. I use this concept to monitor the pH of my system when topping up with Kalk saturated water. I have the controller set to shutoff the Kalk ATO when the pH hits 8.4 - However, by the time the pH sensor reads 8.4 the pH in my tank is past 8.5 - There is a delay in the reading but it's also partly how the kalk saturated water mixes into the tank and where the probe is located.
IMHO - I wouldn't trust a sensor to control/maintain the salinity in my tank. I think that you will be constantly adjusting minor fluctations in salinity either up or down. If your not careful, you may get a bouncing effect.
I also woudn't trust a cheap dosing pump. Thus, I'm prepared to spend the money for a high quality balanced pump setup.
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