hi i have recentally changed over to sand subrate in my juwel rio 125 i have been changing water every week just hovering tube over sand to get bits out but when i put new water in from bucket seem loads more bits sitting on sand so today i clean tank as usual but i then refilled with water through the top of the juwel filter as not to disturb the sand will this be ok ?as it as just dawned on me i'm putting fresh water over all the filter sponges could this lose the bacteria in them ? thanks for any replies ps i have a freshwater master test kit so i can check for all water readings