A heron has eaten all my goldfish and the pond is filling with algae and looking a murky green colour. Should I restock with fish and put in some pond cleaner?
If the heron still looks hungry you should get it some more fish.
A better idea would be a wildlife pond, no fish, plenty of plants including oxygenators and see what turns up. Lots will. You could try the barley straw trick to clear it.
No point in restocking unless you can protect your new fish. A net or wires across the pond can help. Plants that give surface cover, such as lilies, provide cover for the fish and also help to reduce the algae by keeping sunlight off the water. Oxygenating plants are good for clearing the water, and/or you could get a littel solar-powered fountain.