Nope! Sounds to me like you are doing everything right. I do exactly the same as you but use 1/2 the washing powder.
The only time my nappies smell is if I forget the cold rinse a few times or if my machine needs a maintenance wash (I have a washer drier and they are notorious for causing strange smelling nappies).
I do wonder if it is just the smell of the Bamboo as you say. It does have it's own scent which I suppose could be 'pond like'
Hello btw