Small tech. update- I wanted EC/TDS measurement in the sump, and in the mixing tank - but the EZO Atlas EC sensors are super pricy at $230USD each, let alone for 2 of them.
I ended up finding these modbus probes from Renke on Alibaba for $50USD each (RS-EC-N01-3-*-EX), and ordered 2 of the k=1 probes. Should be pretty easy to integrate into the ESPs, and they are rated for continuous read/submersion.
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Will let you all know how well they work out, the main downside is the entire circuit is inside the probe, so once shot the entire thing needs to be replaced, but the entire piece is cheaper than just the probe from Atlas, so not so bad. Hopefully they are accurate. I'll still go with the Atlas probe for pH in the sump, Renke makes one too - but the Atlas is pretty proven.