Dangerous

[Barry P]

Could it be that your testing kit is contaminated.? Did you clean out the tube before use.?

 

[ncjharris]

50ppm can be expected.
During dry periods (despite the rain last night, we are in one) when the water in the resiviors runs towards the bottom, the nasties and chemical readings go up.
Usually seen in summer, but if the winter is dry then this can happen too.