Silk algae will only grow in the N (nitrate, etc.) content is low, the light intensity of ordinary water. So once the fish tank can grow silk algae, congratulations , your water very good quality control.
Nutrition can generate high algae (diatoms, etc.); Too little nutrition, too little light will generate brown algae.
Goldfish looks like green carpet, green carpet also protect their body,maybe they are more comfortable.
I have good water, but I still get the clear gunk and brown algae in my glass. It is never green. My tank is in front of a window and still. Maybe not enough lighting? On my ten gallon, there is dark green algae growing on the sand . I'm sure my plecos and snail are enjoying that. What confuses me is that the tank up there had little maintenance besides water changes and no special lighting. It is not in front of a window, so that confuses me. I guess higher wattage lighting on my 55? Yup definitely, I only have 30 watts in total
You need more higher wattage lighting if you want to green carpet. Lights must penetrate depth to cylinder bottom, Lighting for 12 to 15 hours a day,only a few days you can see the green dot,This is a successful start. Maybe you can see green carpet after three weeks.
But you should pay attention to water temperature, choose your lamp suitable for your tank. Maybe 60 watts total? This is an interesting experiment.^_^