All LECA has manufacturing residues in the pellets. The thing to do is give them a thorough soak before use. My standard treatment is:
- Rinse thoroughly to remove dust.
- Soak for at least 24 hours in a large volume of water, adding 2 tbsp/gal calcium nitrate and/or Epsom Salt to that to accelerate the extraction.
- Drain, refill with plain water to which I've added KelpMax root growth stimulant.
- Soak overnight before use.
At a bare minimum do the first two.
I try to avoid using round pellets if I can, as they move too easily in the pot, making plant stability a challenge.