a lot of nitrates and sufficient light exposure time. i had about 4 watts per gallon before i took all the driftwood out and did a bleach dip, but i did leave them on for 14-16 hours a day. i cut the wattage in half and only run the light on for 8 hours a day now.
found that out the hard way, but learned my lesson. it looked nice while it lasted but the bristlenose couldnt keep up and food/dirt kept getting caught in it.