The sand substrate is coated with bacteria and part of your filtration. New sand isn't and will require some time to become coated with bacteria (Live). This sand can blow around the tank creating a sand storm.
The existing sand not only is coated with beneficial bactgeria, it also contains all sorts of detritus under the upper layer.
(deep sand bed) is 4" or deeper and helps in the denitrification process (converting nitrate to nitrogen).
As I recall, your tank has only been running for about 7 months. Hardly enough time for it to be filled with much detritus if you have a decent clean up crew. My tank has been running for 6+ years. so my dsb
has all kinds of nasties through the layers, that are decomposing.
Take your sand in buckets and keep it covered with fresh sw
, after rinsing it witih sw
in those buckets. Pour off the excess water and add more fresh sw
. That should help retain the bacteria while cleaning the sand of some detritus.