mojoreef said:
I'm not sure, lol. 440 is 440 I agree Collin but thier are other elements that play a role. If his salinity is 1.023 and the other elements are level for that salinity then the calcium is way to high. Alk is but one player in the calcification process.
Mike
As you have elegantly pointed out, calcification by corals is a complicated but poorly understood process. I am certain that there is an optimum balance of all the important elements a coral needs to exhibit optimum health.
Corals though, like any sort of animal, can adapt and also thrive in fairly significant ranges of these elements or other conditions. Ranges quoted for NSW are averages taken from oceans and regions all over the world. Each of the elements making up the NSW will have individual variances around their means depending upon where the samples are taken from.
At some point, in my opinion, trying to achieve the perfect balance becomes an excersize in splitting hairs. This is especially true when considering the fundmental error margin of the tests involved with measuring these values in the aquarium. 400 or 440 for Ca are likely the same value from a statistical perspective using a Salifert test kit. Using a swing arm hydrometer 1.023 and 1.025 may be barely different if many measurements were done and averaged and it was a good hydrometer with no bubbles on the arm. Using a refractometer, these values are clearly distiguishable with a single measurement.
When we start a series of experiments in my labs, the first thing we do is an excersize called a "Gage R&R". This stands for "Repeatability and Reproducibility" of the "Gage" we are using to measure a specific parameter.
In this case, it would be the test kit. To do this one takes at least 3 people and has them repeat an identical measurement at least 3 times. For instance, we could get three people to make Instant Ocean to 1.023 salinity from the same bag and then have each of them measure the Calcium concentration on 3 individual days. To get really technical, we could have this matrix of experiments done 3 times with 3 different test kits in a "blind" and "random" fashion (the user would not know which sample or which test kit he was using/measuring). This would yield 27 total measurements of Ca. From this data set we could understand several important variances. Namely, variances between 1) Workers, 2) test kits and 3) measurements. Also second order effects between permutions of all three sources of variance. Although I have never done this with Ca test kits and IO salt, I am quite sure that the results would be un-surprising. The variance of Ca measurements would be very significant, on the order of at least 10-15% relative for the overall variance.
Only by understanding the precision and accuracy of your measurement system can valid conclusions be drawn from a set of experiments.
The moral of this is when we suggest for a hobbyist to make changes to his tank for small differences in measured parameters, we are mostly dealing with a clear case of statistical uncertainty.
I think the important question here is at what point does the benefit of the proposed changes become negligable with respect to the time, effort and risk involved?
If we are suggesting changes of parameters that are within their variances of uncertainty, then the expected benefit will also be statistically un-measureable by definition.
This is a technical way of saying that at some point we begin to split hairs with parameters.
My suggestion for a best practice regarding aquarium parameters would be for each hobbyist to keep a log of values and watch them over time. If values are within their generally established safe ranges, but a trend is noticed over several weeks, then I would suggest a corrective action to be worthwhile. If on the other hand, parmaters are found to be outside their ranges or deviating from their normal values by large swings, then also I would suggest a corrective action.
For tanks that are healthy and growing with no real problems other than fine adjustment of parmeters, immediate action is not warranted in my opinion. Making changes to tanks carry a small but certain risk. Changes such as this can be carried out slowly over time if desired. However, it is extremely likely that no noticable or measurable benefit will be realized due to the reasons I elaborated on above.
Does this make sense?
Sincerely...Collin