Pond Boss Forums GENERAL QUESTIONS Water chemistry Hardness Questions

Maybe I'm overthinking all of this...

Running through some new tests on my colorimeter (Hach DR870), I cant seem to figure out the hardness. I'm measuring hardness using the calmagite colorimetric method (Hach method 8030). In my city water samples, I have been consistantly getting 3.7 to 3.9ppm total hardness (3.4ppm MgCO3 + .4ppm CaCO3). The same samples read 60-70 on 2 different types of "test strip" methods. Is my city water that low or is there something I'm missing?

With some research, I see that the formal title of the procedure is "HARDNESS (0 to 4.00 mg/l Ca and Mg as CaCO3". Am I right in that 1 ppm = 1 mg/l? if so, why would a total hardness test only read to 4.00? I hope this doesn't sound too rediculous....

I am not familiar with that test method but based on what you have written, I am guessing this is a ow hardness test method with a range up to 4 ppm. That being the case, you are likely above the range of the test in the sample you are reading, and getting a false reading. You shou8ld match the test to the expected range of the test. If you expect 60 ppm, then choose a test method with a range to 100 ppm. You can use this test method by doing a dilution of the sample with distilled water. Make sure the distilled water you use has no testable hardness by running a test on just that water. Dilute the pond sample 1:10 (1 part pond plus 9 parts distilled water). Run the test on the diluted sample and multiply the results by 10. Accuracy depends on your accuracy of dilution.

Yes, PPM is the same as mg/l.
If the test reads in mg/l as CaCO3, then you are set. If measuring as ion, then you need to multiply mg X 4.12 and ca. X 2.5 to get to CaCO3.

Thanks for the info...

It's nice to be able to have a second opinion here! I spoke with Hach and it was a very low hardness test for treated waters. Guess I'll be looking much closer next time!