what exactly is mulm? How should one go about collecting and extracting some to be added to another tank? As far as clearing up that water I would recomend lowering water level to about half so that you get more cycles per hour through your filtration system. Also keep up with cleaning your filter media. Once the water has cleared to acceptable clarity slowly add more water to desired level. If this substrate is that sensitive to disturbance it may be a pain to plant your plants. Just my 2 cents but I have no direct experience with AS.