Pearson's Square (Mix water dH)

I came across this method of working out how many parts to use of two water sources to mix to your required hardness.

I am showing a picture of the spreadsheet model I created based on the Pearson's Square to see what it looks like. If you want to try it, you can download the .xlsx file that is attached.

I tried it and it works. Problem now is how to adjust pH, as it is on 9dH and a 8pH, whereas I require 7.2pH.

The left calculation shown is my actuals. To the right just something to play with. To use the spread sheet, fill in the yellow blocks and do not overtype anything else.



O sucks, can not attach xlsx files. If you want it, PM me an e-mail address.

 

OK, made a calculation error. Fixed now and double checked!

 

This calculation is used to mix your water that you want to prepare and age for a water change.

How you go about it:
Measure the hardness of your two sources of water.
Decide what the final hardness should be.
Input the three values in the yellow cells to the top left.
Decide the qauntity of RO water you want to use.
Enter that under RO Parts, also yellow, middle top.
The value of Tap water parts is calculated in the cell underneath.

The areas to the right is to double check and show the Pearson's sqaure in the box format.

This makes it very easy to see how much tap water to add to your available RO water. In the example above, if you enter 10lt of RO, it calculate that you must add 13.35lt tap water and that your container must be able to hold 23.35lt of water. So you can play around till you at something you like! Mix and test.

 

The final problem is now to adjust the pH to the required pH. I took 50lt of my mix and added 1.25ml of pool acid. My pH was 8 and it stabilized 30 min later at 7.15pH. That was a lucky guess. Whish there was a calculation that could make it more precise and take the guessing out of it. The secret therefore is to start with a very small amount of acid. I actually started too big and could easily have ruined my batch of water. Now to see by how much the ageing and aeration will increase the pH by...

 

Great Post Tom, on a sometimes tricky issue for keepers of Softwater fish, living in an area with local tapwater that is high in PH.