I would like to have enough faith in the salinity probe to be able to do what you're proposing. But first I'd like to see a study on the on-going accuracy of the probe in that given application. Even if such a study were able to show such on-going accuracy, I'd like to know how often the probe needs to be re-calibrated before I embraced the process. What happens if, oops, you fail to do a re-calibration on time? If I were to try it now, I wouldn't do it without using multiple salinity probes doing the testing, and I'm not ready for that expense. I might consider doing it without multiple probes if a number of people who work for Neptune say they have successfully implemented what you're suggesting with one probe. With multiple probes there's also the intellectual challenge of coding a comparison between two probes and acting on the results. I don't think existing Apex code can handle such an equal to or less-than or greater-than comparison.
For now, I'm happy with my Apex based AWC doing 5 gallons a day (not using a DOS) and my stand alone Apex based ATO doing my top-off. As yet, I haven't found there to be enough variability in my system's salinity to merit anything more that a weekly salinity test and a possible manual correction.
ya...I started doubting the idea after I posted it. In reality, I want to replace a very small amount per ATO (like...1% of total water volume at most), and that won't actually move the salinity up to 1.027, that's more like 1.02626 (from 1.026), so it's probably a bad idea unless the probe was remarkably
precise and accurate
I started thinking of just using one optical sensor and two PMUPs to do an AWC instead of the DOS (maybe like what your AWC is?), presuming have have the ATK for topoff. If I put a low sensor on (say, 2 gallons down from the ATK's optical sensor), I could trigger a daily drain with a PMUP down to the extra sensor (with the ATO routine off), then fill to the ATK sensor with NSW and resume the ATO routine. Does that sound like it would work? Way cheaper than the DOS and seems just fine if the programming works. Note: I am a professional software engineer but have know idea what the apex programming is like. I don't know what language, what OS, I don't know if it's all scripted or compiled, don't know if it's a grown-up java type language or all in COBALT...I have some research to do
Sure, maybe doing it slowly with the peri pumps is a little less 'shock' to the chemistry, but really...most people get along fine with 7-14 day WC cycles, I'm hardpressed to think a daily 'shock' is much to worry about.
In other words, if 'normal' in the hobby is 10% every other week and I'm going to do 0.7% every day, I don't really care about the difference between 0.7% daily vs 0.03% hourly...right?
But I welcome your thoughts, and am interested in your AWC setup...
I'm planning for a build next year which will be my first with a real controller, first above 130gal system (currently only a 29g, used to have 90+sump). New system is likely to be a 180g DT + 75 tank as sump + a separate fuge (40B, maybe). I'm thinking I want to try 1% daily changes, and guessing it'll be around 200gal of system water, so about 2gal/day. With near-zero head height (and OSW going to a floor drain), I'm expecting the PMUP can do the whole day's change in about three minutes. My goal is to make it easy so I spend more time enjoying the tank. probably mix a 50gal of NSW per 3 weeks or so.