Salinity effects on test kits

[DonW]

Ive read that Salifert test kits are calibrated to a specific salinity 35ppt or 1.026 Sg. Mine is 1.026 on the refract so actual would be 1.025.

How much of a difference does this make in your Ca and Kh test results?
Does it affect our Ph probes?
Off the subject, does + or - .002 have any effects on corals growth or health?

Don

 

[dwall174]

Along for the ride here!

Being that I just switched over to Salifert test kits & I also keep my SG at 1.025 I’m curious if there’s any deference?

 

[cwcross]

Hi Don,

I don't think these small differences will lead to any significant effect on animal health. pH probes will not be affected because they are monitoring H+ concentrations in water as an absolute. It won't matter what the SG is.

I'm not sure if everyone is aware that SG will vary with temperatere, while ppt won't. A ppt of 35 is a ppt of 35, regardless of whether you are at 70F or 90F. SG, on the other hand changes if the temperature changes because the water expands and contracts, causing its volume and density to change. The change in SG with temperature is pretty strong really. If the test kits target 35 ppm, I would look at that more than the SG. However, that being said, the differences in the readings of the test kit will be accurate enough for government work. In fact, I'm confident that the error in the test itself is probably larger than small differences in SG would cause.

Sincerely...Collin

 

[NaH2O]

One important aspect of salinity comes into play when you are deciding where your levels should be (i.e. Ca = X, Mg = Y, etc). If you want your levels to be the same as NSW, then your salinity would need to be the same.....and figure out the breakdown from there. If you don't want to keep your salinity the same as NSW, then your calcium, etc. levels would need to be based on that salinity inorder to stay ionically balanced. At least this has always been my understanding.....Collin, correct me if I'm wrong.

 

[DonW]

Nikki I'm sure your right about the balance and salinity.
Collin, Thank you for clearing that up. I have a temp compensating refractometer but I dont think everyone does. Can you tell us how temp effects Sg (formula or chart to compensate) or should everyone just target salinity at 35ppt.


Thanks for your time
Don

 

[NaH2O]

Don - I think that most of the refractometers on the market now are ATC, not sure, but when I was shopping for one I had noticed most indicated ATC. On swing arm hydrometers, there are some that have an ATC plastic.

Here are a few articles in the meantime put out by Randy Holmes-Farley (I also need to re-read these to refresh my brain):

Reef Aquarium Salinity: Homemade Calibration Standards

Temperature Corrections for Hydrometers - This article contains a nice chart of Salinity at various temperatures and specific gravities

Specific Gravity: Oh How Complicated!

 

[DonW]

Thats why I replaced mine, I lost the little chart.

Don

 

[kc]

Nikki, what is the cal, alk and salinity balance should be?
As I remember, the NSW is 1.025 for salinity, 420 for Ca and 10 for Alk.
What are these parameters should be if salinity is higher/lower. Is there a formula/chart for it?

Thanks
KC

 

[DonW]

Try this http://www.andy-hipkiss.co.uk/index.htm?http://www.andy-hipkiss.co.uk/cacalc.htm

Don

 

[cwcross]

Yes, Nikki I believe you are correct. Sorry so late but have had a crazy evening/afternoon. Good helpful info you posted.


DonW, Specif gravity is nothing more than a measure of density. Density is mass(weight) divided by volume. As water heats up, it expands so the volume goes up but the weight stays the same. Thus density and specific gravity change. PPT is parts/thousand, which is a unit based on weight/weight. Thus changes in volume associated with temperature don't affect PPT. I think refractometers actually measure concentration of salts, which also changes with temperature for the same reason. I'll bet that the ATC just helps to report ppt from the salt concentration. PPT and concentration are very closely related and oftentimes used interchangebly...C

 

[NaH2O]

Reef Aquarium Water Parameters by Randy Holmes-Farley

KC - I figure it out by percent changes, also think of S=35 really as 35,000, and the elements make up that amount (i.e. 420 of those 35000 are calcium). Find the percent difference between the 2 salinities then apply it to the parameters. As an example: SG = 1.023 or 30 ppt. NSW is 1.026 or 35 ppt. 30÷35=0.86, 100-86 = 14% change. Lets say Ca at S=35 is 420. To figure it out at S=30....420 X 0.14 = 59 then 420 - 59 = 361. Therefore, Ca at S=30 to be balanced is 361. Clear as mud? lol - this is why I'm not a math teacher

 

[cwcross]

I will add too that there are some calculators available on the web that will tell you what balanced levels and CA and ALK are at various PPT and/or SG levels. Just search in google for Kalk calculators and/or ALKalinity calulators or somesuch. You might find this helpful. Sorry I don't have the link handy..C