Hi, I was looking for an equation (outside of the pool math calculator) for adding chlorine to my pool and found this:

Initial chl solution * x = desired solution * pool volume

I tried it out on my pool numbers and checked it against the pool math calculator and it appears to work (at least, I should say the results agree). I was trying to think how to explain this, but I can't really seem to articulate to myself WHY it works. Can someone help me out with this? I can't really figure out what the value is that you achieve when multiplying the desired solution by the water volume.

Thanks (trying to improve my long abandoned math skills).