My fish tank has a reddish brown coating on everything, how do I go about properly cleaning?

I have a ten gallon tank with eight small fish, the largest being no longer than an inch and a half. I recently completly cleaned the tank because it had been a while and the rocks and plants and gl were starting to collect a slimy, reddish-brown coating. I changed all the water, changed the fillter, rinsed the rocks, washed the plants, and hosed out the tank. After refilling the tank, I treated it with water conditioner - I even added a few shrimp to help clean. Everything looked nice and clean for about a week, but suddenly now everything is collecting that reddish-brown slime again! I went through so much to get my tank all spiffy - please don't tell me I'm going to have to do this weekly! Is there sometime I'm doing wrong? If so, what can I do to fix this??