Strange results when testing rocks

So I have a few rocks that I am wanting to put in my tank once it's set up. They passed the vinegar test (I know it's accuracy is debatable) so I also left them in a 2.5 gallon cooler full of water for about a week and a half, with parameter tests before I put in the rocks and now tonight. The strange thing is, both KH and GH dropped. At the start of the test my PH was about 8.0-8.2, GH was 250.6 ppm and KH was 161.1 ppm. Tonight, after a week and a half with the rocks, the GH is 196.9 ppm and the KH is somewhere between 125.3 and 143.2 (it was only greenish yellow after the 7th drop). And there was no change in the PH. I was using API liquid test kits and I retested twice tonight to make sure and got the same results everytime. If I'm not mistaken, the point of the water test is to ensure that the rocks aren't leeching minerals into the water correct? And if they are then the hardness will go up right? Any suggestions? Are these rocks safe to use? Thanks

 

Bumping this up for you

 

Bumping this up for you

Thanks

 

If it's changing your water parameters, they're probably not safe. Take one out and try to scratch it with a steel knife. It it scratches the rock, don't use it

 

The scratch test is to see how calcified it is which would leech into the water, taking up carbonates and other minerals is pretty impressive. Do you have a picture of this rock? I'd be willing to bet that you had something in the cooler and the residue wasn't all gone, or that the same experiment without the rock would give the same result.

 

The scratch test is to see how calcified it is which would leech into the water, taking up carbonates and other minerals is pretty impressive. Do you have a picture of this rock? I'd be willing to bet that you had something in the cooler and the residue wasn't all gone, or that the same experiment without the rock would give the same result.

That's what I was thinking as well. They are just pieces of granite. Nothing special. I'm going to give the scratch test a try as well

 

This is indeed a strange and unlogical result. Granite should be safe.

 

try this start over by letting the rock dry fill two bucket with the same water. Put rocks in one the other is a control bucket then wait a week and see if the water only bucket has changed.