Lava Sand

[kno4te]

If you can verify it’s chemical free then you can use it. Older lava sand had or has chemicals in it which affected pH. You can test the pH in a small container with sand and water. If all it’s stable then all good.

This was brought up along time ago and there were chemicals in it that messed with the pH. Haven’t seen it for a while so maybe it’s different.

 

[twentyleagues]

You can use vinegar to check if it will effect ph. Although muratic acid is a better quicker test. If it fizzes then it will raise ph eventually. If it's clean plain lava rock crushed up it should be fine. Like kno4te says put some in a container of water and test give it a week and test it again.