Thanks for the reply Caryl.
Our pond is in the corner of the section which has a lot of banana trees etc that hang over parts of it, but I have cut these back. I figured without these trees there would be no shade as it is in direct sunlight. You mention that the gunge is natural so obviously if it stops the fish from getting cancer, then it's a good thing. What a good fish person I am - I didn't even know this could happen. It makes sense, but I had just never thought about cancer in fish.
Thank you I will definitely not stress too much about having the green in the water, but I will look at getting oxygen weed and lilies and if the greeness continues, then at least it will look prettier with all the plant life
Thanks again,
Saskia
P.S You have a great looking pond! I'm a little envious but that is because I can see your fish in the clear water!