I believe lava rocks might have nutrients and other materials stick into their structures and might get released later. I'm not sure about this but if lava rocks really do some from volcanoes then I'm sure they would have something in them that might make pH or ppm level fluctuate later on. I would just stick with the hydroton and stay away from the rockwool since Zandor hates it so bad for the same reason I think lava rocks might be bad. Goodluck <3
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