Checking for excessive electrolysis is not just simply putting a probe in the coolant and testing to one ground or touching the side of the radiator. There are several checks that must be made to rule out possible causes. During testing, utilizing a DVM, if the reading is 400mV or greater the vehicle could have any of the following problems:
-Natural occurrence
-Chassis Ground - loose, missing, or corroded
-Engine Ground - loose, missing, corroded, or undersized
-Starter
-Alternator
-Added electrical devices overloading engine ground strap.
If the cause of excessive electrolysis is not determined the inhibitors in the new coolant will deplete faster than normal and also the voltage will seek a ground path. The most likely path would be the heater core, radiator (if metal), or water pump seal; could cause other engine damage.
If you have excessive electrolysis it could be the coolant or it might not. If you do not determine the root cause flushing and refilling the cooling system could only be a Band-Aid.