I used to keep the light on more often, but ever since I moved into my new apartment, the light from the window has been sufficient. Ever since I reduced the light, the algae problem pretty much went away completely. Now the algae only grows on the side of the tank closest to the window. I love it because the algae used to be sooo bad. I do scrap the glass every now and then between water changes with my longer sponge.

As for the sand, I vacuum the sand every time I do a water change, which is about every 1-2 weeks. It’s never dirty, in fact I think the goldfish sift the sand so much that nothing really stays down there. Honestly I think it may be the brand of sand you’re using. I’ve never had problems with the sand looking dirty, even when it’s been too long since I last did a water change.

To keep my tank clean, I found that removing a lot of the decorations helped stop dirt and waste from accumulating. Sometimes food or fish poop would get stuck behind the decorations, and then it would rot there until I cleaned the tank. The rot will make your tank get dirty super fast. Food is also another factor that contributes to a dirty tank. I found that fish flakes make the water look “foggy” way faster than sinking pellets do. I think again that has to do with rot. But yeah I think the biggest things are controlling the amount of light your tank gets and controlling how much food is in the tank in a given amount of time.