Re: HIGH and LOW Nutrient tanks definition....or...What is a LOW and HIGH Nutrient ta
That is a loaded question. And I think you are leaving out one key piece here, coral species - what you have and what water parameters they need.
The way I see it is that you would want to have Alk, Ca, and nutrient levels based on the coral species you have in the tank. It seems like a key component to add to your question.
What are you defining as nutrients? Phosphate and nitrate only. Or do nutrients include carbon, nitrogen, phosphorus, potassium and micro-nutrients (those nutrients that corals need to grow). The reason why I am asking and I think this is important, your question is basically getting at wanting to know what levels you should target for high nutrient vs low nutrient tanks and this ties back into what the needs are for your corals.
I think you will get some varied opinions on what is considered a high vs low nutrient tank and what those levels are. And how those levels correlate to alk and Ca levels will also solicit varied opinions.
It might be easier if maybe trying to understand components of this first. Some coral species hard stoney corals (sps) do better in low nutrient systems, and these are also the types of corals that need higher levels of Alk and Ca because they need to take those in to build their hard skeletons to grow. Other corals, soft corals, can tolerate higher nutrient systems, but they don't need the higher levels of Alk and Ca because they don't take in as much to live or survive, they don't have hard skeletons, thus can do fine w/lower levels of Alk and Ca. What these measured levels are may somewhat vary depending on who you talk to or what article you read.
There are some things that we should keep in mind though, in many ways we try to match the levels in our tanks to the natural environment (and in some instances try to push those boundaries a little bit). What is good to know, are the levels in the natural environment and at what levels sea life no longer can tolerate. That way we know what the boundaries are and what we have to play with in between. Sea life will have a range that they will thrive at and where they will tolerate to survive. There will be a range that they can thrive in and and on either end of this range they will tolerate levels. And then there will be the extreme levels in which sea life will start to die at. Example: Think of it as a bell shaped curve, at the highest peak they will thrive, lower at each end they will tolerate, and the very lowest points they start to die at. You can have any parameter along the bottom axis (e.g. Alk, Ca, Nitrate, etc.). Yes, even nitrate, some corals assimilate nitrate into both polyp and zooxanthellae by direct uptake from the water, so having none at all is not beneficial and can cause death just like it does at extremely high levels of nitrate.
---- examples of natural environ parameters ----
Typical Surface Ocean Value:
Calcium 420 ppm
Alkalinity 2.5 meq/L, 7 dKH, 125 ppm CaCO3 equivalents
Salinity 34-36 ppt, sg = 1.025-1.027
Temperature Variable
pH 8.0-8.3 (can be lower or higher in lagoons)
Magnesium 1280 ppm
Phosphate 0.005 ppm
Nitrate Variable (typically below 0.1 ppm)
Nitrite Variable (typically below 0.0001 ppm)
Ammonia Variable (typically <0.1 ppm)
From literature:
Nitrate - many studies have shown that at higher levels (~40ppm) there are toxic effects to corals. Many critter can tolerate 20ppm, especially fish. Recommend that nitrate levels in corals aquariums should be well below 10ppm and preferably much lower or undetectable on standard test kits for tank w/sps corals. Depending on the LPS or softies you have you may want a range between 10-20ppm (on the lower end for LPS on the higher end for softies). Having mixed coral tanks can get challenging, feeding corals (LPS/softies) can help to keep them living in tanks that are keep in lower nutrient tanks, 5ppm to zero.
Alkalinity - Anything from 2.5-4 meq/L (7-11 dKh) is acceptable. Actually there is no exact target you should shoot for, until you get more advanced. For the most part, as long as you're in that range, you are providing a good environment for your tank's critters. It is also important to know that Alk also affects the amount of calcium and other trace elements that can remain in solution. Higher alkalinity values than that range, and you can run into problems with precipitation. This excess will begin to accumulate on equipment, forming a crust or shell on things like heaters and pumps. In extreme cases, you can even get what appears to be snow in the tank's water column or cloudy water. Lower values will cause instability in your tank's pH level. This may result in constantly lower or higher pH readings. Or even worse, wild swings in the tank's pH. This causes stress on all tank inhabitants leading to a slow demise, disease, or eventually death. If you have a high bioload of corals, you may want to keep the Alk levels of 3.2-4 meq/L.
Calcium - Anything in the range of 380-450 ppm is good. Again, until you get more advanced (especially when trying to maintain SPS corals), any Calcium value in that range is acceptable. Again with more bioload you may want to consider maintaining a minimum of 400ppm, and ideally at levels of 450ppm or higher for sps tanks.
Phosphate - Phosphate values as close to zero as possible are ideal. The problem is, most commonly available test kits out there don't do a really good job of testing true phosphate levels in the tank. Phosphate is always present in the tank though. It's simply a matter of keeping these values as low as possible. The main problem with monitoring phosphate levels is that the majority of phosphate in your tank are consumed by the algae, and therefore are bound into the actual algae itself. This means that most test kits will not take the bound up phosphate into consideration. (I.e. You can get readings near zero, but still high phosphate content in your tank. The majority of it, inside the algae). Best to harvest the algae and get it out of the system.
