Chemistry calculations

[big_ben102000]

hi all,

I recently started dosing sodium bicarb, CaCl2, MgCl2 and Na(NO3).4H2O. I am trying to dial in the dosing calculation.

1g of solute in 1000L of water should give 1ppm/L. but does the molecular weight of the molecule has an effect on the overall ppm/L

thanks !

 

[bertoni]

1g per 1000L is 1 ppm, always, but if you want 1 ppm of calcium and are using calcium chloride, you need to remember that calcium chloride (anhydrous) is only 36% calcium by weight. So it'd be 2.8 mg/L to get 1 ppm calcium. Does that answer your question?

 

[big_ben102000]

hi Jonathan,

yes, but do we need need to consider the Ca reacting with other components in the reef tank that might reduce or increase the variable Ca ?

my readings of Mg is a little off after dosing

 

[bertoni]

I am not sure what you mean. The calcium (or magnesium) will be consumed at some rate by the tank, so measuring fairly shortly after dosing is a good idea. It only took 10 seconds or so for the calcium supplement to mix into my 29g tanks, so I measured very soon after dosing. A larger tank with a large sump might require a bit more time.

 

[big_ben102000]

I am dosing CaCl2, MgCl2 and Na(NO3).4H2O at the moment.
for CaCl2 anad Na(NO3).4H2) the theoretical calculation in ppm increase pretty much matches the actual water testing before and after adding (give or take some ppm.. since hobbyist kits aren't the most accurate) but the MgCl2 the measurements seem to be way off from theoretical calculations.

any opinions ?

 

[bertoni]

How far off are the test results? You might have a bad test kit.

 

[big_ben102000]

hi Jonathan, the readings were over by about 3 folds.
in the last couple of days. I was able to get the my calculation reading to match the test kit reading. i am using salifert btw. I waited 2 hrs before taking a reading again. previously was 10-15 mins.

thank you for the inputs

 

[bertoni]

Okay, if you are getting matches now, I guess I wouldn't worry. The Salifert kit should be good to within 15 ppm or so if it's used carefully.