You may be well aware of this, but for the sake of others a critical part of the measurement is a Kelvin connection, (2 current and 2 voltage spikes) to automatically compensate for lead resistance.
Use a 10-ampere test current and compare readings of several mechanically similar joints in the pool. Maybe compare readings of one pool to those of other [newer?] pools, and establish baseline readings. Without previous readings, there’s not a lot else to do.
BTW, millivolt readings with a constant-current source and an 87 are perfectly good too. I've used 1 to 100 amperes for this job. They are still Kelvin measurements.
