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laurentm
03/17/2006, 07:15 PM
Can fluctuations in Ca ad Mg concentrations affect conductivity?

My conductivity went down (was 52.8, now 51.9) and the only thing that changed, that I can tell, is my Ca and Mg (Ca was 550 after overdosing and is now 420).

Thank you.

bertoni
03/17/2006, 08:48 PM
Such fluctuations will change the conductivity, but the changes will be smaller than the detection limits of hobbyist equipment.

A dosing method can change the SG if dilute enough. Was the 52.8 measured before the overdose? What was dosed?

What is the setup like? Sometimes protein skimmers plus autotopoff result in a drop in SG, if the skimmate isn't replaced with saltwater.

Randy Holmes-Farley
03/18/2006, 07:33 AM
How much did magnesium change?

The calcium change will only drop conductivity from about 52.8 to 52.6 ppm, but there may have been many other changes at the same time.

More than 97% of the total conductivity comes from sodium, magnesium, sulfate, and chloride, and more than 90% from sodium and chloride. So changes in other ions are usually trivial:

Using Conductivity to Measure Salinity
http://www.aquariumfish.com/aquariumfish/detail.aspx?aid=1804