We have a small fish pond and I'm familiar with how to manage it. It has a skimmer and biofilter and all that and the water stays crystal clear with little effort.
But there is a grotto on the east side of the house with a 4 foot tall by 4 foot wide waterfall. All it has is a pump, like a sump pump. No filters, no bio filter or anything. The water gets black and fetid and stinks if you leave the pump off for a day or two. I don't know how to keep it clean. We emptied it out and pulled about 6 inches of rotten leaves and hickory nuts out of it. Somebody had lined the bottom with large stones.
Anybody have experience with anything like this? Any advice?
The "sump" for the waterfall holds about 250 gallons.
The little fish pond also holds about 250 gallons. It almost takes care of itself.