How do you calculate alkalinity change with a water change?

[WildReefGuy]

I want to know how to calculate how much my Alk will raise with a water change. Let’s say I have a water volume of 16 gallons at an alkalinity of 7.3 and I’m taking out 5 gallons and putting in 5 gallons of new water with an alkalinity of 10.0. How much will my Alkalinity raise? Also what is the formula for figuring this out?

 

[EeyoreIsMySpiritAnimal]

Just take out 4 gallons... The math is easier

 

[MNFish]

((11*7.3) + (5*10))/16 which would be ~8.14
So it is gallons left * alk of current plus gallons changed * alk of new divided by total gallons

 

[WildReefGuy]

Just take out 4 gallons... The math is easier

IT HAS TO BE 5 lol!

 

[WildReefGuy]

((11*7.3) + (5*10))/16 which would be ~8.14
So it is gallons left * alk of current plus gallons changed * alk of new divided by total gallons

You da bomb thanks!

 

[Roli's Reef Ranch]

FWIW: this is how you calculate salinity for water changes too

 

[WildReefGuy]

FWIW: this is how you calculate salinity for water changes too

You are also da bomb!

 

[Gtinnel]

Or if you don’t want to do the math yourself

Aquarium Water Change Calculator | BeanAnimal's Reef

Use this aquarium water change calculator to chart how a given water parameter will rise or fall over the course of multiple water changes.

beananimal.com