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after you test your water with a test tube, do you rinse it out under the faucett or wash them with soap in a sink? How does it affect results if at all?
I just rinse out and dry. (air dry or paper towel) Never soap on anything for the fish tank. Prior to testing, just flush the tube & cap out with water to be tested ( fill then dump, fill again then dump, fill again then test). This way any residual water in the tube is water you are testing.