My small pond 5ft. by 2.5ft.and 18″ deep has become muddy and slimey. The slime adheres to the plants (oxygenater, Lilly and Iris) and also floats in lumps on the surface. There were fish in it up to 5 months ago when the heron got them all. It is generally very muddy and disgusting. I have a filter in it but have switched it off for the moment. Should I empty it and start again or is there any treatment for it. Looking forward to hearing from you. Thank you.
The thing to realise about fish is that they excrete nutrients into the water and this encourages algae. If you want fish you must have a good UV filter and, ideally, a bio-filter as well to break down their waste.
Don’t bother emptying the water. Put in a 5cm layer of gravel with some soil mixed … this helps to create a natural cycle, but a small body of water can overheat and produce a lot of algae, although this will settle down.