07-11-2012, 11:43 AM
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Originally Posted by Anthony56
Another way to change the hardness mixing RO/DI water and tap water is by using what is known as the ‘Pearson’s Square’. It is a ratio, in this case, tap water to RO/DI water.
For example let’s say you are looking for a GH of 7 in your tank and your tap water is 12, RO/DI water is O. Subtract the value of the GH you would like from the value of RO/DI and you get 7. That is how many parts of tap water you will need in your ratio. Next, subtract the value of the GH you would like from the value of your tap water and you get 5. That is how many parts of RO/DI water you will need in your ratio. The ratio is 7:5.
Now let’s suppose you are putting together a 40 gallon tank. So, we start by dividing the 40 gallons by 12, which is the total of the parts. The answer is 3.33 gallons per part. Now multiply 3.33 by 7, the amount of tap water needed. The answer is 23.33 gallons of tap water. Subtract 23.33 from 40 and you get 16.67. So you will need 23.33gallons of tap water to 16.67 gallons of RO/DI water to come up with an approximate GH of 7.
If you have fish in the tank then adjust the hardness incrementally. I haven’t used this yet to adjust the hardness in my tank yet so I would check with others as to how to proceed. I was planning on lower or raise the GH on more then 1/2 dH per day. Check with others on this site for a recommendation. Good Luck!
Thank you for posting this. Not having hard water myself I can't experiment with this, but it sounds logical.