Backyard Aquaponics
A place to discuss aquaponics

Hey all,

Wondering if anybody knows how to calculate exactly how many grams of Calcium Hydroxide (CaOH2) or Potassium Hydroxide (KOH) to add to your system to raise it to a certain pH.

For example:

If I tell you I have a 1,000 gallon system with a current pH of 6.5 and I want to raise it to a pH of 7.0, how many grams of either CaOH2 or KOH should I add to reach this desired pH?

Thanks in advance!

I don't about how to calculate it, but I have it written down in my notes that 2 level tsp of Calcium Hydroxide will raise the pH +0.2 in a 1000 gallon system.

Don't know if this helps you or not but you can start there.

The amount of change is going to depend on the system, mostly because of buffering capacity.

You can take a known amount of system water out (lets say 5 gallons for example) and then add KOH until you reach the pH you want in that 5 gallons. Let it sit for a while to see if the pH changes (add more KOH if needed and give it some more time to stabilize) - keep track of the total amount of KOH your adding. Your basically doing a titration. Once the pH is stable, you have a pretty good idea how much KOH it takes to change the pH to what you want, for that 5 gallons of system water. Since you know how much KOH it took to change 5 gallons and you can calculate how much it will take to do the entire volume of your system as long as you know how many gallons are in the system.

I wouldn't place 100% faith in this estimate because things like algae or slime coating the sides of the tank can cause big differences but if you proceed cautiously this should get you close. The buffering capacity of the system can change over time so don't plan on using the same estimate every time.

Hope this helps.

Well thank you both very much for your inputs!