Relationship between SG and Calcium

[Dom]

I spent the good part of yesterday evening reading all the links provided by everyone related to reef chemistry. Thank you!

Is it correct to say; how high calcium (or any nutrient) can be raised is related to SG?

 

[Downbeach]

Each salt mix has a certain amount of those elements incorporated in them, so if you make your WC water at a certain SG, those elements will reflect that level, i.e. if you have a SG of 1.023 your Ca, Alk and Mg will be lower than if you make your WC water to a SG of 1.026.

 

[Randy Holmes-Farley Verified Community Expert]

In fact, it is directly proportional to the salinity (or to the digits after the 1 for specific gravity).

So if your mix matches the tank, and you boost the sg from 1.023 to 1.026, the calcium (and everything else in both types of water) will rise by a factor of 26/23 = 1.13, or 13%.

That would take calcium from 380 to 430 ppm.

 

[Dom]

In fact, it is directly proportional to the salinity (or to the digits after the 1 for specific gravity).

So if your mix matches the tank, and you boost the sg from 1.023 to 1.026, the calcium (and everything else in both types of water) will rise by a factor of 26/23 = 1.13, or 13%.

That would take calcium from 380 to 430 ppm.

I'd been using a measured container to give me a SG of 1.025. Several months ago, I realized my ratio of 5 gallons of RODI to salt mix was giving me a SG of 1.030; high by many opinions. I've since corrected this to give me a ratio that yields 1.023. I've concluded this is why my calcium is so low.

I've again adjusted my salt mix to RODI to get me back where I was; a time when things were thriving.

The moral of the story: If it isn't broken, don't fix it! LOL

By the way; what is the difference between "salinity" and Specific Gravity? I though they were interchangeable terms.


Please explain what I am seeing on the left as opposed to the right.

Thank you

 

[Randy Holmes-Farley Verified Community Expert]

By the way; what is the difference between "salinity" and Specific Gravity? I though they were interchangeable terms.

Salinity is a measure of the total salt in the water, and has units of ppt or PSU (the same for our purposes). 35 ppt is considered normal average seawater, and it contains 35 ppt, which means 35 grams of total salts per kilogram of water.

Specific gravity is the ratio of the density of the seawater divided by the density of pure fresh water at the same temperature. IT has no units, and has numbers like 1.026. 35 ppt seawater has a specific gravity of about 1.0264.

 

[Dom]

Salinity is a measure of the total salt in the water, and has units of ppt or PSU (the same for our purposes). 35 ppt is considered normal average seawater, and it contains 35 ppt, which means 35 grams of total salts per kilogram of water.

Specific gravity is the ratio of the density of the seawater divided by the density of pure fresh water at the same temperature. IT has no units, and has numbers like 1.026. 35 ppt seawater has a specific gravity of about 1.0264.

I understand; Thank you!

I took the liberty of testing my new water BEFORE I put it in the tank. Admittedly, it was at 36ppt. But since my tank currently was sitting at 30ppt, I was okay with it. I tested pH and Calcium. The calcium was up to 440, which made me very happy! However, my pH was also up to 8.4. That isn't terribly elevated, but is up just the same. Should I be concerned?

This reef chemistry stuff is fun!

Thanks again.

 

[Randy Holmes-Farley Verified Community Expert]

Yes, it is fun!

And no, pH 8.4 is no concern at all. Anything between about 7.8 and 8.55 is fine, and the higher end may be preferable except that it accelerates precipitation of calcium carbonate onto pumps and heaters.

 

[Myka]

I took the liberty of testing my new water BEFORE I put it in the tank. Admittedly, it was at 36ppt. But since my tank currently was sitting at 30ppt, I was okay with it.

Yikes! You really should be testing the tank before your waterchange and the mixed saltwater before you use it. Salinity swings aren't good for the corals as you've learned the swings also change calcium, alkalinity (more important), and all the other elements.

In fact, it is directly proportional to the salinity (or to the digits after the 1 for specific gravity).

So if your mix matches the tank, and you boost the sg from 1.023 to 1.026, the calcium (and everything else in both types of water) will rise by a factor of 26/23 = 1.13, or 13%.

That would take calcium from 380 to 430 ppm.

Thanks for posting this - I've been curious about the math behind this. I know anecdotally how much it will change.

 

[Dom]

Yikes! You really should be testing the tank before your waterchange and the mixed saltwater before you use it.

I always test before my WC. I test again, 24 hours after the change.

In this case, it was a smaller WC of a high concentration as I wanted to bring up the salinity. The last WC went from 30ppt to 31.5ppt. Gradual.

 

[Downbeach]

The best way to safely increase your SG in your system would be to use freshly made SW @ 1.026(35ppt) as your top off. Once your DT is at the level you want, to back to plain RO/DI water.

 

[Dom]

The best way to safely increase your SG in your system would be to use freshly made SW @ 1.026(35ppt) as your top off. Once your DT is at the level you want, to back to plain RO/DI water.

Good idea!

 

[Greenstreet.1]

That is one of the reasons I love ESV salt mix

 

[Myka]

I always test before my WC. I test again, 24 hours after the change.

In this case, it was a smaller WC of a high concentration as I wanted to bring up the salinity. The last WC went from 30ppt to 31.5ppt. Gradual.

Oh I see. I was under the impression that you normally do not measure the SG of the newly mixed salt, you just mix using a measure and don't check SG before you use it. Some people do that (which is crazy imo haha).

I also use the "saltwater top off" method as Downbeach describes to raise SG.

 

[Dom]

Oh I see. I was under the impression that you normally do not measure the SG of the newly mixed salt, you just mix using a measure and don't check SG before you use it. Some people do that (which is crazy imo haha).

I also use the "saltwater top off" method as Downbeach describes to raise SG.

Using Instant Ocean Reef Crystals, I've calculated 646 grams to 5 gallons of water = 35ppt. I've marked that amount off in a Pyrex measuring cup so that future mixes are quick and easy. Of course, I check the results before the WC.