How is sludge formed?
Sludge is usually formed due to an abundance of nutrients at the bottom of the pond such as fallen leaves, twigs, dead plants, etc. that pile up over time. If there isn’t enough oxygen at the bottom of the pond (by means of proper aeration, destratification and ample beneficial bacteria), you will have a sludge build up. It’s pretty nasty stuff – dark black, mucky and stinks.