Need advice on setting up a reef tank.

[LabTest57]

Why not change the dosing/mixing directions to mix more salt in order to reach a specific gravity of 1.025 at "70 degrees Fahrenheit", which is closer to the 20 degrees Celsius temperature standard.

From 60 to 80 degrees Fahrenheit, there can be a lot of inconsistencies for +/- changes in specific gravity of the solution w/ the salt mix. I personally find it easier, when one uses a standard with a more accurate value of specific gravity "for which reef tanks can be optimally set-up and maintained at."

At 75 degrees fahrenheit with a specific gravity of 1.021, tells me that the salt mix doesn't contain enough sodium. NSW = 35 ppt of salinty, however, SSW (Seachem Sea Water) = <35 ppt of salinty. Using temp. standards makes it easier to mathematically estimate how much "X" salt mix is needed at "X" temeprature of water/solution. Of course, I can't type the real formula here (any special charatcers are practically unallowed due to symbol restrictions,etc.), however, this will be the first time I use a salt mix that gives me the actual specific gravity at a specific temp. I will try to test/experiment and see how accurate the value really is.

[LabTest57]

[QUOTE=LabTest57;7622] At 75 degrees fahrenheit with a specific gravity of 1.021, tells me that the salt mix doesn't contain enough sodium. NSW = 35 ppt of salinty, however, SSW (Seachem Sea Water) = <35 ppt of salinty. .[/QUOTE]

More correctly SSW yields ~31.43 ppt of salinty. Since Reef Tanks need to be maintained at tropical temps., one would need to add a lot more salt mix at a temeprature of 75 to 78 degrees Fahrenheit. Although water volume will increase, density, however, decreases. If a specific gravity 1.025 were achieveable with this salt mix at 70 degrees Fahrenheit, values between 1.023 and 1.025 (i.e. values less than 1.025, but no lower than 1.023 is possible) would be in the recommended range for the 75 to 80 degree temperature range of most Reef Tanks.

The optimum temperature range is 75 to 85 degrees fahrenheit. Something too low as 70 isn't good, however, it's the lowest average temps. in air-conditioned offices, stores, etc. Something as high as 89 isn't bad, but anything beyond 90 is a bit extreme; however, only corals have been recorded to be able tolerate such temperatures (fish and invertebrates weren't on the list that I reviewed from NOAA...).

You can see why it is neccessary to change the salt mix directions, because hobbyists will go with the recommended, which isn't really the "recommended" i.e. the amount of salt mix based on specific gravity and temperature of the solution/water.

[LabTest57]

I've decided to drop this topic, I hate to start any controversies again. Anyway, I can't comment against those who have a PhD in biology,etc... =)

[Tech Support LK]

Although, you are not interested in continuing this discussion, I think it is important for others reading this thread to understand the difference between measuring specific gravity and salinity and why the instructions on our new Salinity salt are written in the manner they are.

The driving force for Salinity (our product) is the replication of natural seawater, to the very best of our ability. To that end, we have collected data on all the oceans of the Earth, dating back to the nineteenth century. We used the averages of these data to arrive at targets for ionic composition.

Now, some of the targets we aim at are independent of temperature. Others are not. For those values that vary with temperature, we have two choices: we can specify a temperature, or we can specify some relevant parameter that is temperature-independent, such as salinity. In the world of physical chemistry, a standard temperature, and a standard pressure are specified. In the world of chemical oceanography, a standard salinity is generally specified. There are good reasons for that choice. The temperatures of the Earth’s oceans show considerable variability, as you might expect (consider, for example, swimming in the Arctic Ocean, as opposed to swimming in the Pacific Ocean off the Kona coast.) There is variability in salinity as well (see Millero’s Chemical Oceanography, Chapter One, for some informative diagrams), but the variability in salinity is not as great as in temperature. Millero’s Figure 1.14, for example, shows a variability of 33 to 36 ppt over a latitude range from 60 degrees south latitude to 60 degrees north latitude.

Whether this is the primary reason why salinity was chosen for a standard, I couldn’t say. That standard has been around longer than I have lived, and I am loath to argue with every oceanographer now working in the field.

So, we specify the pH, alkalinity, and ionic content of Salinity (our product) made to a standard salinity of 35 ppt. You state that the standard temperature is 20 degrees Celsius: that is news to me. The fact that it isn’t is one good reason not to target that temperature. And since we really are concerned with density, not specific gravity, and density varies with temperature, we do not specify specific gravity as a benchmark.

There are not (as you state) a lot of inconsistencies in specific gravity over the 20 degree Fahrenheit range you quote. There are, instead, inconsistencies in density, which we avoid by specifying a standard salinity.

Specifying a standard salinity has one final advantage. It is quite easy to calculate (if you have the list of raw materials that go into the salt) the amount of salt that ought to be added in order to hit a specific salinity. We calculated, and later confirmed by extensive laboratory work, that 36.269 grams of Salinity (our product), diluted up to a final liquid volume of 1 liter, will give you a salinity of 35 ppt. Of course, you will not be weighing the salt to the nearest milligram, and you will have some uncertainty in the measurement of your total volume, if you are like most hobbyists. But you will find that this quantity of salt added to the appropriate volume of water will, regardless of water temperature, give you a nice, consistent, repeatable 35 ppt salinity. And that target will give you a nice, consistent, repeatable pH, alkalinity, and ionic content, time after time, regardless of temperature.

As for the remainder of your comments, you seem to focus on the wrong variable. Specific gravity is important ONLY insofar as it is representative of density (if corrected for temperature), and density matters ONLY insofar as it affects ionic content (i.e., salinity.) So, when you state that “SSW yields ~31.43 ppt of salinity,” that is true only if you don’t read and follow the directions on the label. We guarantee ionic content at a specific salinity: we do not guarantee results if the instructions are not followed.

I hope this helps. At the least, I hope you can see why it is not necessary at all to change the directions, because salinity (and not specific gravity or temperature) is the key.