I had the same brand from a different supplier.Particle size was 3-6 mmHi Kempster,
Sorry to hear about your bad experience. Here's the link to akadama I bought, it's really good quality
Just as a warning, it's best to sieve and get rid of the biggest "granules". It will make planting easier. And also, rinsing is more important than soaking. It takes a while to get rid of the dust... And don't worry if the water is getting slightly cloudy when flooding the tank, it clears very quickly.
It is really good