I grabbed some settled water out of my top off after it had been in there for a day, though I do use an Osmolator so it does top off from the bottom where there is likely to be some muck from the kalk.. the water is what I found copper in (0.04ppm).
By what method? If a kit, it may not be accurate.
Was it food grade lime? Perhaps switch to a different brand if you think it the source. It is not normally a big source.
This is from my copper in limewater article, where lime precipitated copper, not added it :
Chemistry And The Aquarium: Metals In Limewater ? Advanced Aquarist | Aquarist Magazine and Blog
https://www.advancedaquarist.com/2003/5/chemistry
Precipitation of Copper from Limewater: Experimental Results
The fact that a number of aquarists have reported blue precipitates in their limewater residue suggested to me that there may be something more to this story. Sure, they could have been using especially impure lime, or had especially impure source water. Nevertheless, it was easy enough for me to run some experiments to see what was really happening. In all of the experiments to follow, I monitored copper concentrations using a modern analytical lab technique: Inductively Coupled Plasma (ICP) using atomic emission detection. I used two different emission peaks (324.754 and 327.395 nm).
To start, I made a solution of 1.0 ppm copper as copper sulfate (ACS reagent grade) in deionized water (700 mL). It had no detectable color by eye. When this sample was analyzed by ICP, it had an easily quantified set of emission peaks for copper, and this emission intensity was used as a standard (1.0 ppm).
To this solution I added 2.4 grams of calcium hydroxide (ACS Reagent Grade) and stirred it on a magnetic stirrer for 1 hour. This amount of lime is far more than necessary to saturate this solution (which would take just over 1 g of Ca(OH)2). The solution then settled for 24 hours, and a slightly cloudy sample was removed. This sample was analyzed and found to contain 340 ppb copper before filtration and 133 ppb copper after filtration through a 0.45mm polypropylene syringe filter. The value of 133 ppm copper represents a droop of 87% in the copper concentration.
The original solution was allowed to continue settling for 6 days total, and another sample was withdrawn. This sample was found to contain 160 ppm copper before filtration and 125 ppm copper after filtration through a 0.45mm polypropylene syringe filter.
Additional calcium hydroxide was added to the original solution (2 g/600 mL), the solution was stirred for an hour, and the solution was allowed to settle for 24 hours. This sample was found to contain 33 ppb copper before filtration and 25 ppb copper after filtration through a 0.45mm polypropylene syringe filter. The value of 25 ppb copper represents a drop of 80% from the 125 ppm copper solution just before this second lime addition, and a total drop of 97.5% from the initial copper sulfate solution.
As a control, I tested a solution of calcium hydroxide (2 g/50 mL of deionized water) without any copper sulfate added. In analyzing this sample, I could detect no real signal from copper, either before or after filtering. This result implies that the “natural” copper concentration in these samples is below about 10 ppb.
