DIY Automated salt water mixing system

[Seth81]

Originally Posted by sphelps

Install a conductivity probe in your tank/sump to control salinity, not your salt bin. Setup two tops offs, one from fresh water the other from saturated salt solution. Program controller to use fresh water if salinity => traget, and saltwater if < target. Set alarm if salinity drops below a certain point to remind you to refill salt. You can program a pump to remove water from your display on a timer, set top off control to allow extra top off time during this interval.

Something like this which is what I'm implementing, I've done a few similar ones before but you need a controller like profilux.

I never had issues relating to calcium, alkalinity, or other measurable elements as far as I could tell. Auto water changes were kept small and on a daily bases to prevent large swings and they system also had a reactor or dosing system due to high demand.

I have a PLC based control system, so most of this isn't a problem, the only challenge I would have is finding economical conductivity/salinity probes that output either a 4-20mA signal or a 0 - 5 VDC signal. Any one have any suggestions? I looked on ebay and found some rosemount ones...but too much money.

Also isn't it better to do larger water changes? I personally do weekly 10% changes. But after doing some math it seems to me larger less frequent changes helps in reducing pollutants

I really like your idea of adding a high point drain to your RO/DI tank, I may do the same for some added reassurance that I don't flood anything if a relay decides to stick (even though I'm using SIL rated relays).

I personally prefer the third tank setup I'm using rather then two and mixing SSW in the sump, just for the added reasurance I guess... but realistically I am sure we all have a single point of failure in our reef setups that could cause a crash.

Also isn't larger less frequent water changes more effective in reducing pollutant levels? I personally do weekly 10% changes.