[fkshiu]

Having rocks in a rubbermaid puts them in complete darkness. This will help kill off anything photosythetic such as nuisance algaes.

Secondly, you'll have a much easier time removing the crud that the rock will slough off. This crud contributes to increased phosphates and nitrates which, in turn, feeds nuisance algaes. If you change the water out of the rubbermaid on a regular basis, you are denying the algae its food source.

The whole process repeated over the course of several weeks or months is known as "cooking" rock. This is opposed to simply "curing" the rock which only involves cycling the rock through an ammonia spike. Cooking is a much longer and more labourious process, but it can achieve much more than curing. Cooking is not necessary with a new tank and "fresh" live rock from an LFS, but can be a last resort to someone fighting a never ending battle with algae, cyano, etc.

If you've purchased "old" live rock some someone getting out of the hobby, you often find yourself dealing with very poorly maintained live rock full of crud and crap and covered with various types of undesirable algae. In fact, you just may have bought the reason why the seller gave up the hobby in the first place!

Some people take even more extreme steps such as lowering/increasing both the salinity and temperature of the cooking rock to further dissuade algae from returning.

Again, cooking is not required for a new live rock, but simply having new live rock in a dark container for a few weeks before putting it into the display is always helpful as it pretty much ensures that you don't have to stare at an empty tank and you won't get started on the wrong foot.