Does anyone have any experience at usinf chert rock as a substrate,
Does it leach toxins?
Does it affect pH
Any info is appreciated.
Oh, I tried googling, and it only had info on geologic timescale leaching/ dissolving.
I haven't tried chert, unless some of the rocks I have used were chert. It doesn't seem to contain anything that would leach out in water. You could always put a small amount in a bucket, add water, measure the KH/GH/pH of the water, let it sit for several days, then re-measure the KH/GH/pH and see if they change.
Can you take a water sample to your LFS and have them test it for you? Most LFS will do water tests for free and there shouldn't be a problem going back in a week or so and having them re-test another sample for you