I just ran 13 hours at a continuously monitored 1 mA of current (OK, it ranged from 988 uA to 998 uA, and this appeared to be linearly temperature dependent), using 12 gauge .9999 electrodes spaced 1.5" apart and submersed 5" into a full 32 ounces of 1.5 uS distilled water, and my calibrated Hanna PWT is currently reading only 8.5 uS. The CS is perfectly clear, with no Tyndall effect viable to me via a red laser pointer. I have cut off the process at 8.5 uS.

I have a quite small level of white and also some black floaters and also some of the same that have sank. Any recommendations for extracting the CS from between the top and bottom crud?

The device I used is home made, and is based on the LM334Z constant current voltage regulator and using 68 ohms for the resistor. My power supply is a 30V DC transformer. My stirring method is via a home made magnetic stir plate and a PTFE coated magnetic stir bar.

Monitored voltage fell progressively throughout (faster at first, and then progressively slower at the later stages, so I'm assuming that there is a log function here somewhere), and voltage was clear down to 9.50V at the cut-off point. At the warmest period of the day my current output read 998 uA, and at the coldest it read 988 uA. The LM334Z is fully capable of holding current quite constant. I did not bother to add a temperature compensating diode and resistor leg to my circuit, and this is why as the room temp. fluctuated by about 4-5 degrees F the uA's ranged from 988 to 998.

My only disappointment was in not achieving a full 10 ppM (10 uS) after running a full 13 hours.