KH Calculation

[malau]

Hi all..

Can anyone tell me the forumla how to do the calculation as follow:

Tank: 33.1 L Original KH 7.448 (Hanna)
Removed water 2.6L to 30.5L
Add new water (14.224 KH). i.e. water change and make it back to 33.1L

New KH is 8.12

Just wonder what is the formula to calculate the new KH?

Thanks

 

[steved13]

There are calculators for this, but you can use simple arithmetic.

I'm pretty sure this is correct:

30.5 x 7.448 = 227.164

2.6 x 14.224 = 36.9824

227.164 + 36.9824 = 264.1646

264.1646/33.1 = 7.9802537

slight variances in the numbers (2.5l instead of 2.6l for instance) or testing accuracy would be the reason for the difference between 8.12 and 7.9802537

 

[malau]

Thanks so much... couldnt make it work before

 

[malau]

Just wonder in the last step the 31.5 value is a constant?

 

[steved13]

Man, I'm Sorry, that was an error...I don't know where I got 31.5 from.

You probably get it now that it's correct but just in case...30.5 is tank volume after the 2.6 is removed, 2.6 at the new KH is what you'll be adding back in and the 33.1 is the new tank volume after the two are added together.

I've corrected it above, I think it's right now.

 

[malau]

Really thanks again. The value of 2.6L is estimated as I marked the water tank volume by each cm in height.... so yeah maybe thats why the calculation is slightly different. It is helpful

 

[steved13]

I gave that as an example, but I'd be more suspect of the testing. The Hanna checker accuracy is within 5% so that would be in the range.

The math is really just averaging, same thing as 50 people with $1 and you add 50 more with $2 what's the average... $1.50 50x1=50 50x2=100 100+50=150 150/100=1.50...it's a little intimidating when you throw in measurements we're not used to (KH liters), and decimal points...but it's the same math.

Glad I could help

 

[malau]

One thing I forgot is that 33.1L is included the displacement of the rocks ...etc (if I use the term correctly) maybe thats why the ans is slightly different

 

[steved13]

Could easily be a contributing factor. Anything varying will cause inaccuracies in the final number in the math.