Chaeto Reactors compared to Algae Scrubbers, part 3
Now for nutrients.
Nutrients are defined as inorganics, not organics. The word "nutrient" is sometimes confused with "nutrition", and maybe in restaurants the words might mean the same thing, but for aquarists they are totally different. Nutrition food particles are mostly visible, but nutrients are invisible, and for aquariums the nutrients are:
Organics: These are food particles, and most of them big enough to see. They can be apples, pellets, nori, baby brine shrimp, flakes, peanut butter, poop, mucus, leaves, twigs, fish eggs, and other types of detritus, all of which are eaten/consumed by some type of organism. Organics are usually very visible when concentrated, and only after the organics get digested by a long chain of animals and bacteria do organics become invisible inorganics (this is called “remineralisation”, because they are now basic minerals once again). Organic food particles (which include waste) can be large, small, or dissolved, and if dissolved in water then the water may be cloudy or clear. For example, if you take mucus and blend it in water, the resulting dissolved organics would be invisible. Natural reefs are very highly loaded with organics, especially at night (sometimes a night diver cannot see his own hand because of the camera light reflecting off of the mass of particles). Lakes even more so, so much that sometimes you cannot see more than a meter underwater in full daylight. Aquarium keepers however tend to want ultra “clear” water, where all the natural food particles are removed from the water.
Algal Structure: The structure of algal cells make the algae thick or thin; solid or soft. The thinner the algae is, the more surface area it has, just like small particles of sand have more surface area than larger pebbles do. This increased surface area has more contact with water around it and thus can pull in nutrients faster. And the softer the algae is, the less structural cellulose-like material (like celery) it has. Hard structural cells, like celery, are great for holding a shape but bad for photosynthesis because there are less photosynthetic cells like there are in a leaf; so harder/stiffer algae absorb nutrients slower. Therefore for faster nutrient absorption, you want thin and soft algae.
Chaeto: Has a firm structure that holds it's shape, and is about 1 mm in thickness. Nutrient absorption is slow.
Green Hair: Has a soft structure that does not hold its shape, and is about 0.1 mm in thickness. Nutrient absorption is fast.
Slime: A different category altogether.
Light: Photosynthesis does all the nutrient filtering, and it requires light; if the light is reduced, then filtering is reduced. Two facets of algal cells can alter the light: Translucency and self-shading. Translucency is the ability of light to go through a strand of algae; if light can do this, the light can reach cells further inside or on the other side of the strand and do more filtering there. Self-shading is when one strand of algae shades another strand; when this happen to a large degree, the growth of inner portions of a clump of algae slows down or dies, as outer growth is added over it. Thus the clump may appear to be increasing is size but the inner portions will actually be dying and putting nutrients back into the water, sometimes faster than the newer outer layers are taking the nutrients out of the water. And the larger the clump is, the more the inside starts dying. Only the outside portion grows.
Chaeto: Non-translucent (opaque), with high shading of other strands.
Green Hair: Medium to high translucency, with medium shading.
Slime: Low translucency when thick, and high shading.
The graphs of the following study show the light-blocking characteristics of chaeto: "Production within dense mats of the filamentous macroalga Chaetomorpha linum in relation to light and nutrient availability"
Fig 5B shows how, under bright light, chaeto productivity (filtering) drops 72 percent with just 2 cm of chaeto thickness. And this does not take into account any dying chaeto underneath.
With green hair algae however, the green hair filaments are very thin, and translucent, so light and water flow spread throughout the algae, thus maximizing filtering. No part of the algae is "on the dark side of the growth" like it is on almost all parts of chaeto.