I have a system which allows me to adjust the pH of my well water (i.e.: raw water). It’s a new system, and it’s time for the first refilling of the alkaline solution tank which serves to balance the pH of the raw water so it is correct at the tap. And soon, it will be time to refill the alkaline tank. But, the recommended ratio of soda ash to water makes my pH too high. If I give the SDopers the numbers, maybe they can help me figure out the correct ratio? I think I have enough info for this to be an easy enough calculation.
a) My raw water is a pH of 6.0
b) The recommended “recipe” for the alkaline solution makes the water a pH of 8.0
c) The “recipe” for the alkaline solution is: fill a 16 fl oz cup with soda ash powder (using the cup as a scoop) for every 5 gal raw water - until the alkaline tank is full. It holds 50 gal. (Not sure, but we may need to know the denisty of soda ash to convert the fluid ounces [volume] to the weight ounces.)
As I mentioned above, I discovered the “recipe” mixture was too rich yielding a pH of 8.0 at the tap. This gives the water a soapy feel, so you never know when you’ve washed all the soap off your body! It is annoying, so… Eyeballing it, I removed 15 gal of alkaline solution and added 15 gal of raw water. Sure, I could eyeball it again this time, but this is wasteful and a pain in the neck. This gave me about a pH of about 7.0 at the tap.
Based on this info, can someone help me calculate what my new “recipe” would be to get about 7.0 at the tap? Ideally, I’d like to know the ratio of soda ash (in fluid ounces - using my scoop) for every 5 gals of raw water.
Where are all the Sdoper Chem E’s? This should be a piece of cake! It’s something that was beaten into you in Freshman Chem! Titration, titration, titration…and all those concentration calculations! C’mon, SDopers! Put on those thinking caps! Even a rough answer should be a no-brainer! - Jinx
The best I can figure, this is just a math problem. The instructions are for your alkiline tank are 1 cup for every five gallons. You have a 50 gallon tank so filling the tank would require 10 cups of soda ash.
There is an important factor that you leave out. You do not say how full the tank was when you removed the 15 gallons. This is important because I can’t figure out how much soda ash was left in the tank after you removed the 15 gallons.
Assuming that the tank was full when you reoved the 15 gallons, you removed 30% of the soda ash. That means you want 7 cups of soda ash for a full tank, or approximately 1 cup for every 7 gallons of water.
I do know this: The pH of well water changes over time. When first drawn, the water in my well has a pH of about 4.8. Leave it 12 hours in a glass, check it again, and it will be 6.5. An aquarium book explained why this is so, but I don’t remember the details.
How one would calculate the amount of soda ash to add to reach some desired final pH I haven’t a clue. I wrestled with this for a while and did some reading because we have fish tanks and pH can be a concern. Before I found a solution, I observed that our fish didn’t seem to care about pH. There was no need to let the water sit out overnight or treat it, so I abandoned efforts to educate myself further.
Do you have some special reason for wanting your water to be neutral? Ours works fine for bathing, cooking, drinking, the fish aquarium and so forth.
WTH, I thought someone had answered this. Did the hamsters eat the replys for lunch? Anyway, there’s a couple of problems with trying to just calculate an answer.
First, the buffering capacity of your water source is an unknown. It’s probably got carbonate in it, with a pK of around 6.5, but there could be other buffering species, or metals with insoluble hydroxides in there as well.
Second, your soda ash powder isn’t pure. Sodium hydroxide leaches CO[sub]2[/sub] out of the air during storage, so as much as 20% of the weight you think is NaOH, is actually sodium carbonate. The mixture won’t titrate your water as well as pure NaOH, plus as mentioned above, carbonate is a buffer.
The upshot of this, is that you’re better off figuring out the right mixture empirically. Since removing 15 gal of alkali from the 50 gal tank, and replacing it with water got you about where you’d want to be, I’d expect that you only need about 70% (1 -15/50) of the ash your recipe called for. That’s 112 oz per tank or 11.2 ounces (7 tenths of a scoop) per 5 gallons.
John Carter of Mars, thanks for the thoughts. Our house has copper piping. The acidity of the raw water will slowly destroy the piping system. For example, it has already eaten through a steel tank component of the water treatment system itself. (This is a slow process, and not worth the cost of installing a stainess steel tank.) I can play with the water until I get the balance correct in the pH treatment (plastic) tank, but it’s a pain.
Using a crude method, I figure I replaced 15 gallons of treated water in the pH balancing tank with 15 gallons of raw water to get the tap near 7.0 pH. That means 70% of the water by volume is treated and 30% was not. Basically, that works out to adding 1 bucket of raw water after every 2.333 buckets of treated water; where one bucket = 5 gal. What a pain! 1/3 of 5 gals is 1-2/3 gals… [(That’s 1.5 gals, 1 pint, and 5.3 ounces! …because my bucket ain’t that incremented!) …Or, I’ll have to see what crazy combination of measuring cups I can put together to find the 2/3 gal mark on a cleaned-out gallon milk jug.]
Working it the other way to cut back on the soda ash, I assumed the original “recipe” = 100%, and I was cutting it down which equates to using 70% of that (35 gal treated/50 gal total). So, then I said if the “recipe” requires a 16 oz cup, then I must need 70% of 16 oz! That’s 11.2 oz.
The tricky part is trying to measure these odd-ball measurements with things found around the home! Surely, there’s a more scientific way, but this empirical method might just work. I’ll let ya know!
Oh, Mr. Mars, one explanation for letting water sit to raise the pH is that gasses dissolved within the water tend to lower pH. The gasses will escape when the water sits causing the pH to rise.
Jinx
P.S. Our fish did best when we did nothing at all to their water, as well!
hey, thanks Squink! You’ve validated my results! I was crunching through the numbers as you were posting, more than likely…hence my previous post unintentionally repeats your findings! Cool! I’ll be trying it out this weekend. If you hear there was a mad run on bottled water in the Mid-Atlantic, you’ll know why! - Jinx
I’m barging into your thread to ask how you test the pH of your water at home. We have a treatment system (acid water and copper piping too!), and I’m not convinced it’s working well.
first things first : pH of 7 means [H+] concentration of 10^-7 ans so on.
using the simple formula : N1V1 = N2V2 (N1 is the normality of the soda solution, V1 is the volume added to V2 of raw water - assuming V1/V2 to be constant). We have a problem of increasing N2 from 10^-8 to 10^-7. So obviously N1 must be 10 times lower.
So my recommendation : Use 1/10 th of the Soda you put in before. YES I MEAN 1/10th - pH scales are logarithmic. And density really does’nt make any difference in this calculation.
- Jinx