How to calculate Alkalinity Dilution by a water change ?

[SomeHappyFish]

I don't know if Dilution is the right word but yeah...

Let's say my Tank is at 10.9 dKH with a volume of 45 Gallon and I do a 10% Water change with new saltwater with a dKh of 8.6.

Mathematically, what should be my resulting dKH ?

 

[Randy Holmes-Farley]

Alk will be the weighted average.

0.9 x 10.9 + 0.1 x 8.6 = 10.67

 

[WalkerLovesTheOcean]

Yup, 10.67.

 

[KrisReef]

Simple dilution = 10.67 dKH

Ho lee I got it rght!

(Weighted Average- Thanks for the term!)

Edit: Forgot to show my work

 

[SomeHappyFish]

My test results gave me a 10.5 dKH, so Mathematically I'm on the right path.

Thanks guys !