Some of the Botanicare products are organic, meaning heavily based on carbon. Bacteria eat carbon and reproduce like crazy in a moist environment with warm temperatures. The slime on container walls could be algae if the container isn't light tight, but it also could be layers of bacteria. It's interesting that you say you change your water every week but still have slime on the walls. For Botanicare products, it could also be layers of nutes that gather on the walls, as organic ferts are known for lumping together and creating a slime that can plug up tubing in hydro. If the grow is good then I wouldn't worry about it much. You might find that the continer stinks, in which case it's odor-producing bacteria. You might find green or grey looking chunks in the water, in which case it's algae. If you don't find either, then it's probably just fert sticking to the walls.