I'm tired of trying to get the scum marks and slime from the fish tank when doing a weekly clean, it looks gross so does anyone have any tips?
You can buy long-handled scrapers or hand-held scrapers with a steel blade. Something like this: http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=26097
My husband uses the handled type in our 30 gallon tank and the non-handled one in my 4 gallon tank. (He also has a magnetic one hanging around for when he doesn't want to stick his arm in the tank.)
You can probably find them locally in a specialty fish store and possibly at your mainstream pet store.
The other thing to consider is that goldfish produce more "waste" than most other kinds of fish. http://en.wikibooks.org/wiki/Animal_Care/Goldfish (See the "Aquarium Conditions" section). Part of your problem may be that your tank is too small for how much fish (even if just one) you've got in it. We definitely had a harder time keeping our 4 gallon clean than the 30 gallon. You could try, in addition to finding the scraper of your choosing, doing partial water changes twice a week instead of just once a week.
What about a magnetic cleaner?
These work by having a cleaner on the inside, and a magnet on the outside. You move the magnet to move the cleaner and it wipes off the algae and muck.
Just watch out you don't move it too fast, and it falls off inside. You can also slide it all the way up to the top, to take it above the water line and reach in to clean the brush.
You can always get an algae eating fish, like an otocinclus or similar fish.
These algae eating fish come in a variety of shapes, sizes, and colors to suit your needs. They often just attach themselves to the walls of the tank and slowly eat away the algae. They do well solo, or in groups and are very docile.
Or you can get a snail, like the commonly sold mystery snail. Just like the otocinclus, snails just travel around eating left over food and algae.
In addition to those, bottom feeding catfish like cory cats, will suck up food and algae from the bottom.
All three work great alone or together, I often have all three as cleanup in my tanks.