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.

Mike