Well I have been told by some "experts" what I do does not work.
Well, I have had the same coolant ( soluble oil) for over 10 years and never drained it, only added due to evaporation.
I use a black light on the tank . I do this where the coolant is returned and the sump is stirred up. I do not use the Hurco Sump, but use a separate tank ( 5 Gal )
You have to be careful as the black light bulb ( 40 -60 watt) gets pretty hot and will explode if anything is splashed onto the hot bulb, The bulb is where no splashes occur and the raw coolant spread out returning to the sump and about 12 " away . You do not want to look at the light ! Cover the tank.
If I have not used the coolant for awhile , it will go pink with bacteria. I turn on the sump pump and circulate the coolant for an hour before I run the Hurco.
it is cleaned up by then . You may want to run it more often to have it ready for action at any time. Coolants go bad due to organics, make sure no food every gets in the system.
The light is on when ever the coolant pump is running.
Rich
If you shut off coolant flow to your work, you want to have a bypass and have the coolant flowing back into the sump to keep maximum light exposure