This is fortunate because green hair algae is the exact type of algae that grows automatically in a properly constructed algae scrubber. Some models also use up-flowing air bubbles. This version, which is basically the exact opposite of the waterfall, allows the algae scrubber to be placed underwater in the aquarium, sump or pond, instead of above it. This greatly simplifies construction, since the device does not need to be waterproof, and it allows placement of the scrubber into tight areas where there is no room above the water line. The design also keeps the algae from drying out in the event of a power failure, because all the algae is under water, and the design also removes almost all splashing. The up-flowing bubble design falls into three categories: those that attach to and shine through the aquarium (or sump) glass; those that float on top of the aquarium, sump or pond water surface; and those that go completely underwater like a submarine. Generally, and except for specific continuous-filtering or continuous-cultivating versions, algae scrubbers require the algae to be removed ("harvested") periodically from the scrubber. This removal of algae has the effect of removing undesired nutrients from the water because the algae used the nutrients in order to grow. The algae is generally removed either:   For waterfall versions, the screen is removed from the pipe and cleaned in a sink with running water. The pipe is removed also, and the slot is cleaned with a toothbrush, to remove any algae that have grown up into it. After the algae are removed, the screen and pipe are put back in the scrubber. For upflow versions, the cleaning method depends on the type:  Glass-attached version: The magnet portion outside the glass is removed, and the inside portion is lifted out of the water. If the growth is thick green hair algae, then it is just removed by hand. If the growth is thin green hair (as occurs in freshwater) or dark slime, then the inside unit is taken to the sink and cleaned with a toothbrush. After cleaning, the inside and outside parts are put back into place on the glass. Floating-surface version: If the growth is thick green hair algae then it is just removed by hand by lifting the LED lid up and pulling the growth out. If the growth is thin green hair or dark slime, then the floating portion is taken to the sink and cleaned with a toothbrush. Drop-in version: The entire unit is lifted out of the water, and the lid is removed.