Compensate for the increase of salinity from dosing Magnesium?

[Oberst Hajj]

I just started dosing Magnesium and it is raising my salinity. Should I be compensating for this increase in any way (removing saltwater and replacing with RODI?)?

Thanks,

Keith

 

[Diesel]

Posting some test results as how much you dose and what they were prior dosing and what they are now due to dosing will help.

 

[Randy Holmes-Farley Verified Community Expert]

Unless you are making a large correction to magnesium, the salinity effect is not large and is much smaller than calcium or alkalinity dosing. In any case, monitoring salinity is always a good plan.

 

[Oberst Hajj]

Thanks for the replies guys.

Well, digging through my Apex Fusion logs, it looks like my salinity has crept up over a much longer time span. So it does not look like it is soley related to my Mag dosing. My salinity did go up 1.7ppt in 24hrs, but Mag went from 1250 to 1400 during that same time frame (my dose program was a little more aggressive then I thought).

I assume I should swap in some more RODI to bring it back down slowly?

Unless you are making a large correction to magnesium, the salinity effect is not large and is much smaller than calcium or alkalinity dosing. In any case, monitoring salinity is always a good plan.

I've never notice an increase in salinity from dosing Cal and Alk in the past. Should I have?

 

[saltyhog]

Can your salinity probe be calibrated and if so how long has it been since it was? Instrumentation error should always be considered unless you've confirmed the salinity changes with another method.

 

[jsker]

Thanks for the replies guys.

Well, digging through my Apex Fusion logs, it looks like my salinity has crept up over a much longer time span. So it does not look like it is soley related to my Mag dosing. My salinity did go up 1.7ppt in 24hrs, but Mag went from 1250 to 1400 during that same time frame (my dose program was a little more aggressive then I thought).



I've never notice an increase in salinity from dosing Cal and Alk in the past. Should I have?

I learned not to use the Apex conductivity numbers as my standard, you are better off using a calibrated hand held refractometer or a fancy digital refractometer to get your true salinity. My digital reads 33ppt and my Apex reads 37.6 today.

 

[Oberst Hajj]

I use the Apex as a guide as I could never get it to calibrate close to my refractometer readings (1.026 on the refracto shows as 27.8-ish on the Apex probe). I checked my salinity with the refracto and it also shows it as being high. I re calibrated my refracto and got the same high readings. Tonight I removed roughly 1.5 gallons of saltwater (I've got a 60g cube and 20g sump) and let the ATO add the removed amount with RODI. My salinity dropped 0.2ppt and then climbed right back up 0.2ppt in a span of 10 mins All per APex logs).

I stopped dosing the Cal tonight as well. I still need to dose Alk as it is pretty low.

 

[Diesel]

Drop the apex probe, they are inaccurate in most cases.
Rely on your refractometer.
Be sure that if you have a redsea meter to calibrate everytime you test, they are just the worse.

 

[Randy Holmes-Farley Verified Community Expert]

FWIW, after using a typical two part to boost alk and calcium for one year of adding 8 ppm of calcium and the accompanying 1.1 dKH of alkalinity per day, there is roughly a 32% rise in salinity over a year using this addition rate without water changes. That boosts 35 ppt to 46 ppt, or sg = 1.026 to 1.035 (assuming no water changes or any other salinity impacts)

If you boost magnesium by 200 ppm using a typical additive, salinity will boost by ~0.8 ppt (for example, 35 .0 to 35.8 ppt) or sg = 1.0264 to 1.0270.

 

[Rjmul]

FWIW, after using a typical two part to boost alk and calcium for one year of adding 8 ppm of calcium and the accompanying 1.1 dKH of alkalinity per day, there is roughly a 32% rise in salinity over a year using this addition rate without water changes. That boosts 35 ppt to 46 ppt, or sg = 1.026 to 1.035 (assuming no water changes or any other salinity impacts)

If you boost magnesium by 200 ppm using a typical additive, salinity will boost by ~0.8 ppt (for example, 35 .0 to 35.8 ppt) or sg = 1.0264 to 1.0270.

Great information. Here I am worrying about adding 45 ppm magnesium.

 

[fugatze]

Apex gets air bubbles in it. Very lightly give some taps on the probe. Watch in amazement as the ppt changes seconds later.

 

[Lionfish hunter]

FWIW, after using a typical two part to boost alk and calcium for one year of adding 8 ppm of calcium and the accompanying 1.1 dKH of alkalinity per day, there is roughly a 32% rise in salinity over a year using this addition rate without water changes. That boosts 35 ppt to 46 ppt, or sg = 1.026 to 1.035 (assuming no water changes or any other salinity impacts)

If you boost magnesium by 200 ppm using a typical additive, salinity will boost by ~0.8 ppt (for example, 35 .0 to 35.8 ppt) or sg = 1.0264 to 1.0270.

Does the rise in specific gravity from magnesium dosing (brs magnesium sulfate or their magnesium mix) throw off the ratio of the other salts in seawater like 2 part dosing does? Basically, can you forever adjust specific gravity using freshwater to compensate for the rise in specific gravity from magnesium dosing to stay at 35 ppt and keep all the different salts at the proper ratios?

Also does all for reef and kalkwasser dosing raise the specific gravity at all?

 

[biom]

Does the rise in specific gravity from magnesium dosing (brs magnesium sulfate or their magnesium mix) throw off the ratio of the other salts in seawater like 2 part dosing does? Basically, can you forever adjust specific gravity using freshwater to compensate for the rise in specific gravity from magnesium dosing to stay at 35 ppt and keep all the different salts at the proper ratios?

Yes, it will change the ration between ions, with exception of ratio chloride to sulfate if the proper magnesium mix is used. I think keeping Mg above salt mixture levels quite challenging because you need to adjust it after every WC.

Also does all for reef and kalkwasser dosing raise the specific gravity at all?

In longer term, no. They will be consumed / incorporated into coral skeleton.

 

[Randy Holmes-Farley Verified Community Expert]

As Biom noted, it keeps the big boys, chloride and sulfate in balance, but not others. But in general, this effect is VERY small for routine maintenance compared to the calcium chloride and sodium carbonate additions.