Algae analogy, quote from Julian Sprung "Reef Notes" vol 1

The best description I have read to describe the problem and how to approach algae....

"If you think of your aquarium as being like a stereo system (pay attention now, I am not kidding), nutrients can be equated with the power (on/off) button, lighting with the volume dial. and algae growth with loudness of sound. When the power is "on" if you increase the volume dial, the sound will become louder. Likewise, in the presence of nutrients, the more light (intensity) you provide, the more algae will grow. Conversely, if the power button is "off", the volume dial may be turned "all the way" and no sound will be emitted by the speakers. It follows then that with no nutrients present, lighting can be increased without proportional increase in algae growth. The algae will not grow at all if the limit, "no nutrients" is reached. It is nice to analyze things like this in the theoretical sense because sometimes their nature is more apparent when carried to extremes. Of course, in a closed system it is impossible to achieve "no nutrients", and a lighting increase will bring about a proportional in crease in algae growth. However, limiting available nutrients does reduce the magnitude of the proportional increase. Therefore, reducing all potential nutrient sources, (i.e. make-up water, detritus, etc) will have noticeable affects on algal growth."

"Interestingly, another factor affects the potential algal growth in an aquarium, ant hat is the presence of algae! Carried to extremes again, of course in a sterile aquarium even with nutrients, will not grow algae. While this may seem obvious, there is more to the presence of algae effect and it affect on algal growth. Not only do you need algae to grow more algae, but also the more algae you have, the more algae will grow. This "snowball" effect is what makes hair algae problems so devastating. There are 3 principle causes for this effect. First is that more algal mass will release more spores and gametes which, given enough nutrients, will continue to grow. Second is that algal mass itself is nutrient rich or put another way, algal mass is a potential source of nutrients. Third is the sneaky ability of algae, by virtue of their design, to trap detritus, which is another potential nutrients source. Algae accomplish this by slowing the velocity of water flowing over them, a trick which makes detritus fall out on them. Dense algae and ones with a surrounding growth of fuzzy filaments trap detritus like mechanical filters."

"In an aquarium full of algae, for instance, a test for ammonia will read "zero", and a test for orthophosphate will probably also read zero. Bacterial decomposition of the plant tissue liberates usable nitrogen and phosphorus for additional plant growth, and nutrients added by the aquarist are rapidly incorporated into the plants. Thus an aquarium full of algae, and an aquarium with no algae can have very similar nutrient levels in the water. If we could "boil these tanks down," however, we could see the difference. The nutrients are not so much stored in the water as they are stored as a potential nutrient source, in the rock, detritus, and the living plants. The quality of the nutrients stored in the algae tissue, varies with the availability of these nutrients. This is at least a part of the reason why the suggested "R.O. treatment" takes a long time to have an effect for some aquaria, when for others it is immediate."

"So now we see how that nutrient levels in an aquarium are not merely a water quality, but actually a whole system quality. With this idea in mind it should be clearer, why I recommend being conservative with system inputs (food, make-up water) and liberal with system outputs (water changes, detritus removal, prefilter cleaning, and algal turf filtration)."