The pumice is not in a pot, but still in the packaging, and I haven't put any water on it.

Is this yellow pumice a problem or sign that the pumice is cheap/bad quality? I am not sure as a lava rock is supposed to have quality?

And does the same apply to perlite?

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It could be;

There will be various natural colour changes in the pumice that is being mined. The colour indicates the type of minerals in the rock. Pumice is almost white because it is naturally low in minerals. Lava rock is the opposite it is made up of melted minerals like iron, & zinc. Just a little bit of iron in it will stain it yellow. Or it was the top layer that has been exposed to sunlight over the few to millions of years sitting in the ground.

That pumice got wet at some point, then it was exposed to the sun. You will notice all of the pumice in your pots with have stains like this on them. It is both the hard minerals in the water &/or algae that grew when wet then left stain when it dried. I seriously doubt it is algae stain.

  • It looks like a water stain to me. If it were a natural change mineral content all side would be yellow and more pieces would have various grades of color – user27862 Feb 4 '20 at 18:50

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