I had the same problem but after talking and reading lots I cam to the conclusion that Crystal bio is soft and can buffer the water as to its compand.
This process makes the media disolve over time producing fines in the water.
With BHM you have it for life…..
Crystal bio also needs a small amount of maintence but BHM is better left alone to eat the poo!
I still dont know where the poo goes? As far as I know Koi only eat around 17% of proten so maybe the poo goes back to the pond and the fish get a second go at the food. maybe this is why the fish grow so much?
I have a report done in Japan which I will find and post…. it shows the BHM was around 20% better of processing waste over a 12 month period.
I really dont know, all I know and can comment is on my results…