I have had this gravel for over 20 years Richard. Its a mixture of 2ml and 5ml, its very smooth infact its your favourite gravel you mentioned a while back somewhere,its the very light in colour "Dorset" gravel,the stuff you can't get anymore,its like gold dust but your absolutely right finer grade would be better all way through but I have bred and kept Hystrix on it for many years and they are ok with it, even the smaller ones can bury themselves so all is good.....thanks for your concern!..oh and thanks for the compliment LOL !!