Goldfish and Angelfish

Question
I have an aquarium with a goldfish and an angelfish, and I have to change the whole water every week because to me it seems too dirty-so every week i take out the fish and cleen the whole aquarium. also every week I get green and brown stuff on the walls of the aquarium and the decorations. how can i keep the aquarium clean for at least a month or so???
Also, i wanted to ask you how to feed my angelfish more, because the goldfish eats most of the food I give them...
Please don't tell me that Goldfish and Angelfish are not copatible because they are very good friends...
Thank you very much.     :)

Answer
Do not change the whole water.  It will kill your angelfish.  If your angel fish gets sick this is why.  You can get a scrub for the greenish brown stuff(algae).  Try to find a food your goldfish hates, but your angelfish loves.  You can try chichlid pellets.