water quality confusion

[guppychao]

just a bit confused and a bit curious on water quality.

 

most of you know that in the ocean, where there are no nutirents there are also none to limited life. however in nutirent rich areas, there is a variety of life including reefs.

 

in our fish tanks, i heard of 2 different sides. somewhere on RC i read that a persons sps were loosing color because the water was too clean, however on the other spectrum i and others strive for pristine water conditions with zero nitrates, phosphates, etc...

 

so my question is what do they mean nutirents? i kind of leaning toward more dirty water as the chemical aspects makes sense, however i am no chemist.

 

thoughts? not sure if there is truly a correct answer as there are probably different aspects that i am probably missing.

[Brian Ward]

The chemicals need to come out, but too clean generally means overskimming, too much carbon, etc. Removing things that the coral feeds on will cause it to lose color.

[ctenophore]

The difference between our tanks and wild reefs is free nutrient rather than low (or high) nutrient. On a reef, like a rainforest, all nutrients are bound up in living biomass, mostly phytoplankton and zooplankton, and there is a huge amount of it. Similarly, in rainforests, most nutrients are bound up in trees. In our tanks, often there are significant free nutrients, which are what cause problems with algae and coral death. A mature or balanced tank has "tight nutrient cycling", meaning that there are many little mouths to instantly uptake free nutrient and turn it into living biomass. This results in spawns, more little critters, etc. All of this feeds corals, moreso than I think most people realize. That's why some corals fail to thrive in otherwise "perfect" water- they may have enough light, low free nutrients, but not enough "extra" food in form of whatever little critters are swimming around or spawning. This is the basis for the "probiotic" approach with the bacteria and biopellets- they allow bacteria to uptake all available nutrient, then break free in clusters and float around to become coral food or skimmed out. In an imbalanced tank with low biodiversity, nuisance algae or cyanobacteria can become the dominant nutrient sink, resulting in insufficient coral food and an ugly tank.