Magnesium raises salinity

[StrategicReef]

I have used DIY Mg and techM both do the same thing, if I attempt to boost the MG Level by 50ppm or so the salinity raises from 1.026-1.028, within an hour.. And it will keep going if I keep dosing.
I had to take some salt water out to compensate.

I am using a refractometer.
It seems to work fine other than that but I am confused am I the only one with this issue?

 

[Mike O'Brien]

Well you are adding a salt. Most of the additives we add are salts.

 

[asl4me76]

Have you attempted to "drip" it into the system vs just dumping it into the system to see if it will help keep your salinity more stable? It's just a thought, but if you are dumping it in ... and you've noticed it is giving you this issue, then I'd consider "dripping it" into the system.

 

[StrategicReef]

I have dripped also and it is the same..
and it's not just a phase.. the salinity stays high..
In the process of raising 150ppm MG I have taken out about 5 gallon of salt water out of a 100G system to compensate.

 

[Randy Holmes-Farley]

A 100 ppm addition to magnesium with any brand of additive (except maybe Seachem which may be higher due to their unusual recipe) will add about 0.4 ppt to the salintiy, so 35 ppt to 35.4 ppt, or sg 1.0264 to 1.0267

 

[Randy Holmes-Farley]

if I attempt to boost the MG Level by 50ppm or so the salinity raises from 1.026-1.028,

That is a measurement error of some sort, either of the magnesium added, or the salinity. The effect is much smaller, as I note above.

 

[StrategicReef]

Well.. I can do those measurements easily.. I dose 100ml of Tech M should increase 100G of water by by 18ppm MG.
And MG did increase in the appropriate amount accordingly.. While I believe your formula I do not think I have made too groos of a mistake in measuring.

 

[Randy Holmes-Farley]

The testing methods may just have limitations on their precision.

 

[wayne in norway]

As a note following a lot of recent discussions on refractometer accuracy it seems that MgCl seems to have a different effect and rate of change on RI than brine though that does seem rather a large jump for a small hump.

Boomer once provided comparative number for RI versus ppt for 'seawater' and brine, it would be interesting to see a similar scale for MgCL.

 

[LifeAquatic]

Thats weird. I just recently dosed 4 bottles of tech m to my tank over the last month and have not had any type of salinity increase.

 

[Randy Holmes-Farley]

As a note following a lot of recent discussions on refractometer accuracy it seems that MgCl seems to have a different effect and rate of change on RI than brine though that does seem rather a large jump for a small hump.

I agree that is a real difference when using a refractometer, but it is not large enough to explain the observation made above.

For example, 10 weight percent magnesium chloride has the same refractive index as 14 weight percent seawater solids. Likewise, 10 weight percent magnesium sulfate has the same refractive index as 11 weight percent seawater solids. So the apparent effect with a refractometer will be a bit bigger than the real salinity increase.

 

[phuzzykins]

I observed a 0.002 increase in salinity from a ~ 180ppm boost in Mg in my system.

 

[Randy Holmes-Farley]

I think that is probably a bit more than it really was, but that is probably within the expected range of precision and accuracy for an ordinary refractometer.

 

[StrategicReef]

I know you guys will say my measurement is flawed but which one out of the Magnesium Chloride or the Epsom salt contribute to the salinity increase?
I got barely half a drop of techM on the refractometer and the salinity is so high it is out of range, the whole thing is completely white.

Also I have the $50 refractometer, do I need the $120 refractometer to measure correctly?

 

[HighlandReefer]

The $50.00 Range seem to work well enough for most hobbyists.

Magnesium Chloride and Magnesium Sulfate (epsom salts) will both add to the salinity.