The grey colour is likely to be caused by the break down of any organic material such as plants, fish food etc. You certainly need to get the fish out and get the crud out before returning them.
I think that's a rather rude response to hogweed. I hope it wasn't meant to be, but that's how it reads. It's a tiny pond to have any kind of fish in. It'll get very hot, very quickly, as others have said. Goldfish can grow very big too.
It's a place where beautiful isn't enough of a word....
I live in west central Scotland - not where that photo is...
A water feature that small is always going to be problematic to keep in good condition. If you have room for a water butt I'd be inclined to fill that up, even with tap water, and change a bucketful or two every couple of weeks. If you can fill with clean rainwater so much the better, but there can be so much airborne crud brought down in rain that tap water is probably safer if it's been left to stand for a few days.
Although you already have fish in there it would be easier to keep healthy without them as there wouldn't be any feed going in or 'output' from the fish to break down.
Oh dear. I don't think that anyone intends to be rude. It's a pretty little barrel but too small for fish unless you can run air into it 24 hours a day. You have pots in there which take up space but not enough of the plants that release oxygen into the water. I think a filter would keep it clear but you have to remember that algae IS natural. Also, you will need to heat it in winter. And finally, goldfish are tiny when you buy them but they soon grow and will need more space.
Posts
It's a tiny pond to have any kind of fish in. It'll get very hot, very quickly, as others have said.
Goldfish can grow very big too.
I live in west central Scotland - not where that photo is...
https://www.livescience.com/11037-goldfish-grow-30-pounds.html
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.