Hi there, yeah I have a 15kg bag of substrate ready to put in the tank - just need to wash it. I don't think it got in the photo but there's three plants that I have in the tank - probably needs more I think. I got my filter online but I don't think they did when I bought the fish. I just had a simple sponge filter with a powerhead on top (10 litre tank) I've had my tank for 4 years now yeah I can see the algae now.
The plant matter was more for the fish to eat because they need some in their diet. Duckweed is a small floating plant that goldfish like to eat. It grows rapidly, uses lots of nutrients, and will help reduce algae problems.
If you have algae growing, then add more live plants.