The float does work with a solenoid and timer to control how long it can activate for and when. I could have added another electronic float but that just seemed pretty pointless as the tank also has a overflow drain so worst case involving that mechanical float is I waste a little water.
The saturated solution method is just something I came up with a few years ago and I experimented with it on a couple tanks I was caring for. I never looked much into it to see if others have done it so I can't suggest any links. The idea is for auto water changes but rather than storing a large container of say 100 gallons or constantly having to refill and mix up a smaller container this method utilizes your controllers salinity probe if available and uses up very little space. You use a container around 20 gallons as the example above and you add a full box of salt. You obviously end up with supersaturation but with proper settings controlling display tank salinity, the controller will switch between the two top off containers to keep tank salinity constant. You can then program a pump to remove water from the sump directly to a drain and the two top offs keeps salinity constant. Best of all, all that's needed is every so often is to add another bucket of salt when you notice little to no undissolved salt. The key is setting an alarm when tank salinity drops too low which will turn off the pump that removes water encase you forget to add more salt from time to time.
The only concern I had before I tried it was relating to solubility of various elements in the salt causing a constant imbalance. However, I constantly measured a system over a year and saw no noticeable fluctuation of measurable elements. It's probably not much different than only mixing a small portion of a salt container per water change which is common practice.
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