Algex & Alumabrite can both be applied between 35"F - 2"C and 80"F - 27"C. The lower the temperature, the slower the cleaning and brightening will be and the longer you will have to wait. The higher the temperature the faster the action but when the temperature is at the higher range, you also have to be careful that the products do not evaporate before they have had a chance to work.
When working with Algex, it's helpful to cover the area with plastic to prevent evaporation and allow the chemical to work long enough to remove the growth. When working with Alumabrite, it's important to do a test in an inconspicuous spot to determine the right concentration and amount of time to leave the product on. If it starts to dry before you rinse it off, you will get streaks. If left on too long, especially in elevated temperatures, it will turn the aluminum white.
When you are through cleaning your aluminum, consider protecting it with Alumetron. This clear coating is easy to apply, very durable and will keep your aluminum looking clean and shiny for years. It's not an anti-fouling. To reduce the attachment of marine growth you need VS721.