Salinity & The Elements

[Johnny C]

I was inspired to post after reading the "Water Quality" thread. A few weeks ago a friend and I did a little water testing after being baffled by why Calcium & Alkalinity were low after a fresh water change. We tested a batch of thoroughly mixed Oceanic salt, and found that Calcium & Alkalinity levels differed substantially with slight adjustments to the salinity:

At a specific gravity of 1.024, the water tested to:

Calcium: 400PPM
Alkalinity: 7.6dKH / 2.51meq/L
Magnesium: 1200PPM

At a specific gravity of 1.0265 (35PPT), the water tested to:

Calcium: 460PPM
Alkalinity: 10.2dKh / 3.66meq/L
Magnesium: 1410PPM

I was pretty surprised to see how much of an impact a slightly higher salinity had on these elements. I didn't test pH, but I wish I would have! Needless to say, I am making an effort to keep my salinity at 1.026 so I don't have to dose two-part nearly as much. I have been struggling to keep my Alkalinity over 8dKH, and I think my low(er) salinity had a huge impact on that. I know that the proper salinity for a saltwater aquarium is subjective, but I wouldn't be surprised if I see a noticeable impact on growth because of it.

Just some food for thought. :fish1:

 

[Gary Majchrzak]

don't even bother to test Ca, alk and Mg unless S.G. (specific gravity) is 1.025-1.026 (which equals 35 ppt salinity)

 

[Johnny C]

Unfortunatly I already did!

Some people keep their aquariums at a slightly lower or higher salinity than the "average" 1.025-1.026 SG. This thread is an attempt to show those people the major differences between those salinity levels, and why they might be having issues raising "the big three".

 

[Gary Majchrzak]

a bonus:

a bonus:

skimmers work more efficiently @ SG 1.025- 1.026

 

[GMaquarium]

Thank you for testing and sharing your results. It may help folks.

 

[Gravesj1s]

Yeah,thanks.
I just got a little bottle of calibration solution to check my refractometer.Check it tonight.

 

[tmz]

Sg 1.024 is 32 ppt which is roughly 91% of the the 35ppt at 1.026. So everything should be about 9.1% less.
Assuming no testing noise and an evenly mixed salt:

if magnesium is is 1410ppm at 1.026, it would be 1283 ppm at 1.024;

if calcium is 460ppm at 1.026, it would be 419ppm at 1.024.

Alkalinity of 3.66meq/l(183ppm or 10.2dkh) at 1.026 would be 3.33meq/l(167ppm or 9.3 dkh.

It appears the alkainity testing is off significantly for some reason.

The point , however,is important and there is no reason to keep a reef tank at less than the nsw value of 1.0264 but not just for calcium, alkalinity and magnesium levels which could at least be adjusted with supplements.
There is an even more pressing reason to maintain nsw sg.. Invertebrates are isotonic and have no ability to osmoregulate as marine fish do.
Marine fish have an internal sg of about 1.008, lower than the water around them(hypotonic) They drink lots of water and pass concentrated urine to maintain their internal sg at 1.008 in water where the sg is higher than that in their body. They can't , however tolerate sg lower than their internal sg for long periods of time since they can't expell the fluids that would flow into them.
For invertebrates which don't regualte internal fluid levels, their internal sg changes to that of the water around them as fluids diffuse into them in an environment where the sg of the water is lower than their own. Conversely, fluids flow out of them in water where the sg is higher than their own internal sg. A shift in internal sg shifts all the internal chemistry and at some point the isontonic animal can not maintain homeostasis and dies. While invertebrates may have some variable range of tolerance in internal sg (not much past 1.023 on the low end ,ime)it's prudent to aim for the optimal nsw sg of 1.0264, in my opinion.

 

[IronMan72]

skimmers work more efficiently @ SG 1.025- 1.026

Why do skimmers work more efficiently @ SG 1.025- 1.026? Does the efficiency of a skimmer continue to operate more efficiently as as SG increases?

At a specific gravity of 1.0265 (35PPT)...

What are you using to measure SG to such precision?

Sg 1.024 is 32 ppt which is roughly 91% of the the 35ppt at 1.026. So everything should be about 9.1% less.
Assuming no testing noise and an evenly mixed salt:

if magnesium is is 1410ppm at 1.026, it would be 1283 ppm at 1.024;

if calcium is 460ppm at 1.026, it would be 419ppm at 1.024.

Alkalinity of 3.66meq/l(183ppm or 10.2dkh) at 1.026 would be 3.33meq/l(167ppm or 9.3 dkh.

It appears the alkainity testing is off significantly for some reason.

The point , however,is important and there is no reason to keep a reef tank at less than the nsw value of 1.0264 but not just for calcium, alkalinity and magnesium levels which could at least be adjusted with supplements.
There is an even more pressing reason to maintain nsw sg.. Invertebrates are isotonic and have no ability to osmoregulate as marine fish do.
Marine fish have an internal sg of about 1.008, lower than the water around them(hypotonic) They drink lots of water and pass concentrated urine to maintain their internal sg at 1.008 in water where the sg is higher than that in their body. They can't , however tolerate sg lower than their internal sg for long periods of time since they can't expell the fluids that would flow into them.
For invertebrates which don't regualte internal fluid levels, their internal sg changes to that of the water around them as fluids diffuse into them in an environment where the sg of the water is lower than their own. Conversely, fluids flow out of them in water where the sg is higher than their own internal sg. A shift in internal sg shifts all the internal chemistry and at some point the isontonic animal can not maintain homeostasis and dies. While invertebrates may have some variable range of tolerance in internal sg (not much past 1.023 on the low end ,ime)it's prudent to aim for the optimal nsw sg of 1.0264, in my opinion.

Thank you for this very detailed explanation, your posts usually answer my next three questions as well as the original.

 

[tmz]

You are welcome.

 

[der_wille_zur_macht]

Salinity & The Elements

This would make a good band name.

 

[tmz]

Sounds like a 50's/ 60's vocal group.

 

[Johnny C]

What are you using to measure SG to such precision?

The salinity was tested using a Hanna Digital Refractometer.

 

[acdraindrps]

Why do skimmers work more efficiently @ SG 1.025- 1.026? Does the efficiency of a skimmer continue to operate more efficiently as as SG increases?

Could be why freshwater tanks dont use protein skimmers. :thumbsup:

 

[der_wille_zur_macht]

Higher SG = more surface tension = bubbles are more persistent, allowing for more time for proteins to stick. acdraindrps, you're pretty much correct re: fw tanks. Try running a skimmer in freshwater some time, it's pretty disappointing. Kinda funny though, since at least two or three times a year in the DIY forum, someone posts a thread "what's wrong with my DIY skimmer? I tested it and it doesn't make any foam!" Sure enough, they're testing in tap water. . .

 

[GMaquarium]

not to get off main topic here but there are freshwater skimmers. They make pond foam fractionators.

 

[boosted chemist]

Good read, i think no i will try to keep my salinity higher, as soon as i get rid of this damn swing arm hydrometer lol.

 

[tmz]

An informative article on skimming:

http://reefkeeping.com/issues/2006-08/rhf/index.php

This from it:
1. Why does skimming work better in saltwater than in freshwater?

There are two fundamental reasons that skimming is more effective in seawater than in freshwater. One is the reduced solubility of organics, especially hydrophobic ones. Because many organics are less soluble in saltwater than in fresh, they are more easily squeezed out of it to an air/water interface, and collected as foam. This is the basis for the well-known salting-out effect of proteins. Quoting from a basic biochemistry text: "At sufficiently high ionic strength a protein may be almost completely precipitated from solution, an effect called salting-out."

A second reason for less efficient skimming of freshwater relates to bubble formation and coalescence. It turns out that air bubbled into seawater forms smaller bubbles than if the same device bubbled into freshwater.1-4 The possible reasons for this have been discussed in the scientific literature, but the exact reason is not universally agreed upon.

Despite the fact that skimmers usually produce larger bubbles in freshwater, and that organics are often more soluble in freshwater, it is not impossible to skim freshwater. Rivers from certain areas of the northeastern United States sometimes have foam on them, which comes from tree sap and other natural organics that enter the water. They have a low solubility in water, and are easily collected as foam in a natural skimming action.

 

[solRNY]

The salinity was tested using a Hanna Digital Refractometer.

hey johnny, sorry for this OT, been wanting to get one of those digital refractometer but hastitant on its ease of use, can you share some thoughts on it:
repeatablity?
how fast for a measurement?
this unit versus an neptune conductivity probe?
likes, dislikes

 

[Johnny C]

The Hanna is awesome, but to be honest I'm a fan of most everything they make. It's surely easier to use/read than a handheld refractometer, but it's also 3x the price. It's also very accurate, calibrations have been dead-on. HTH