Your Ca is 95ppm x mol CaCO3/ mol Ca = 40.08+12+3x16/40.08 = 2.5dennis said:OK chemistry people:
I just got a LaMotte Ca test today and 2 runnign 2 tests I get the same answer of 95ppm Ca, read as ppm Calcium Hardness as CaCO3.
In the following equation used to find the ppm of Mg, does the Ca in ppm number need to be converted from my reading of 95ppm as CaCO3? If so, I would divide by 7.143?
GH in ppm - (2.5*Ca in ppm)
--------------------------- = Mg in ppm
Any help is appreciated!
95/2.5= 38ppm Ca++
The above equation off hand appears right.
Say the GH (total hardness as CaCO3) is 120ppm.
120-95 = 25ppm Mg as CaCO3 equivalents.
25/4.1= ~6ppm Mg.
I'd not bother with this, knowing the difference between a few ppm in a ratio is not going to do much for you unless you desire to add very small, potentially limiting amounts.
Nothing I've found suggest a ratio of Ca/Mg does much, the amount of error in our testing and habits plays a much more significant role I would suggest.
Add a little of both Ca/Mg to your tank each week beyond the amount of plant growth requirements, say 10ppm of Ca++, and perhaps 4ppm of so of Mg++ and you are set. That's in addition to the Mg/Ca in your tap water, other sources.
I recently bumped my Mg up with Rotala wallichii, unlike Edward's photo's, it did not stunt. I am using soft water(KH = 2) and low GH's.
5.4 grams in 1 teaspoon of MgSO4*7H2O.
9.9% of it is Mg.
So per gram of Epsom salt added to one liter: 9.9/100= 99 ppm or mg/L.
So per gram added to a 75 liter(20 gal tank) 99ppm/75= 1.32 ppm Mg++.
5.4 x 1.32 ppm= ~7ppm of Mg.
I added 1.5 teaspoons, a fair amount of Mg to such a small tank.
10.5ppm and that does not include the fraction for the tap.
Generally 1/4 to 1/2 teaspoon per week will address any Mg issue.
But those with higher GH's, likely can use more if they want without issue.
I have not done enough with Mg to say much still.
I only did the Rolata test once. I waited for 3 days after.
So who knows just yet.
Still, adding the rec's I suggest are fairly light, not excessive, if you apply the EI notion to 2x the weekly build up if no Mg is used, then the amounts end up in the 2-6ppm range generally.
Folks have been using Mg in PMDD and with other mixes for a long time.
I tend to suggest a few degrees of GH for soft water, about 3-4 at least using SeaChem EQ or the Gh booster, folks with harder GH waters may need some Mg or Ca to balance things out so neither is limiting.
I think you can approach it that way, using just GH and adding a bit more with a balanced product or................you can analyze GH individually into the Ca and Mg sereprate nutrients.
I'd stick with one method though, that will simply things.
At the end of the day, I do not think you will see marked differences with either method.
Both can supply the required amounts of Mg and Ca.
One test more, the other uses a GH kit or none at all.
Simply because you do not test, does not mean you need to know what the ppm of Ca/Mg, only that you have enough to prevent limiting conditions.
That's the real issue for 99% of aquarist, not confusing themselves with test kits/methods.
Why test unless there is a problem?
How do you avoid such problems to begin with?
Pretty straight forward.
If you suspect K+ is limiting, then add more K+ and see.
You do not need to test the K+, you can if you want, but you do not need to do so to know the K+ is limiting or in excess. Simple calculators will tell you that.