[bguile]

Lee,

I purchased a box of Arm & Hammer baking soda in preparation for future freshwater dips. I mixed some of it with make-up water to drip for a hypo tank but found that when I mixed it, the pH actually dropped. Is that right? Did I buy the wrong stuff? It says sodium bicarbonate and that its for baking, cleaning and deodorizing.

[leebca]

Did you check the pH of the water you used to make it up with?

The use of pure Baking Soda to raise the pH of pure water is such that it takes as little as a pinch to make the adjustment from 7.0 to 8.x. The use of the Baking Soda is for adjusting fresh water.

In saltwater the Baking Soda reacts with salt water constituents and the buffer to alter alkalinity. It is too weak in this chemical mixture to act as a pH control. It has a different reaction in pure fresh water. A small amount in fresh water raises the pH.

If you want to control pH in a hypo tank, you'll need a stronger base. In this chemical mixture, there isn't the concern about the relationship of pH to calcium, magnesium, and alkalinity. I use a strong base, such as sodium hydroxide because I have access to it as a chemist. I don't know what strong bases you have access to or what is commercially available for what you have in mind.

[charlie]

What about the use of washing soda w/baking soda? I used 6 parts baking soda -1 part washing soda as a buffer. That and along with kalk for ph control. Any thoughts?

[leebca]

Washing soda is hard to find in its pure form. So many have additives that it isn't useful. But if it can be found, then what that is, is sodium carbonate. It is a much stronger base, but it does alter the alkalinity.

Actually, sodium carbonate (washing soda) can be made from sodium bicarbonate (Baking Soda) by cooking Baking Soda in the oven.

[bguile]

As far as pure water goes, I'm waiting for my RO/DI unit to ship now. I am using filtered water from a 98% rejection drinking water system which I guess is a lot different from a 99% DI system. I measured the pH before adding the baking soda and it read 8.4. After adding a 1/4 teaspoon to a half gallon of the water, it read 8.1.
Would limewater be considered a stronger base? I have a couple cans of that on hand.

[leebca]

That source water you're using might be a bit tricky. Not sure what might be in it. Did you continue to add some more Baking Soda after the first addition showed a drop? Sometimes the 'pure water' is 'confused' about pH and it takes some ions (the Baking Soda) to show its true pH.

Limewater is a weak base also. Good for boosting alkalinity (also weak in that area) but not for pH control. You can bake some Baking Soda in the oven if you want to convert it to a stronger base.

[bguile]

No. I didn't add any more after the initial drop but I'll give it a try. Is there a certain amount of time or result I'm looking for to say that the baking soda is baked?

[leebca]

I was afraid you were going to ask for details. I had to scrounge up my (very) old notes on it.

Spread Baking Soda (2 cups) on a baking tray and heat in an ordinary oven at 300°F for one hour to drive off water and carbon dioxide. Overheating is not a problem, either with higher temperatures or longer times. This converts Baking Soda (Sodium bicarbonate) to Washing Soda (Sodium carbonate). Dissolve in pure water.

This is, remember, going to affect the alkalinity and not just alter the pH.

[bguile]

Originally Posted by leebca

I was afraid you were going to ask for details. I had to scrounge up my (very) old notes on it.

Spread Baking Soda (2 cups) on a baking tray and heat in an ordinary oven at 300°F for one hour to drive off water and carbon dioxide. Overheating is not a problem, either with higher temperatures or longer times. This converts Baking Soda (Sodium bicarbonate) to Washing Soda (Sodium carbonate). Dissolve in pure water.

This is, remember, going to affect the alkalinity and not just alter the pH.

Best to get the right information while it's available, right? I understand that as the alkalinity goes up so does pH and calcium goes down but does this matter in the QT?

[leebca]

Basically not. However if you're performing a hyposalinity treatment, you don't want to put things into the water that will change the salinity out of the target salinity to effectively treat the disease.

[vaporize]

Originally Posted by bguile

As far as pure water goes, I'm waiting for my RO/DI unit to ship now. I am using filtered water from a 98% rejection drinking water system which I guess is a lot different from a 99% DI system. I measured the pH before adding the baking soda and it read 8.4. After adding a 1/4 teaspoon to a half gallon of the water, it read 8.1.

Not sure if this was answered, but I remembered reading from another thread, if your water is actually too clean of ions, the pH shown by your pH meter might not be a correct one (i.e your 8.4 before baking soda), the water might not have enough ions to provide the electronic equipment a stable reading. Therefore when you add the baking soda, it's actually starting to provide the ions, thus giving a real reading.

[bguile]

Originally Posted by vaporize

Not sure if this was answered, but I remembered reading from another thread, if your water is actually too clean of ions, the pH shown by your pH meter might not be a correct one (i.e your 8.4 before baking soda), the water might not have enough ions to provide the electronic equipment a stable reading. Therefore when you add the baking soda, it's actually starting to provide the ions, thus giving a real reading.

Can you explain? If I'm reading this right, your saying that if my reading of 8.4 goes down after adding baking soda (bicarbonate) to 8.1 or lower that my pH was not really 8.4?

[vaporize]

Originally Posted by bguile

Can you explain? If I'm reading this right, your saying that if my reading of 8.4 goes down after adding baking soda (bicarbonate) to 8.1 or lower that my pH was not really 8.4?

As explained by LEE to me from before, your RO or "almost RO" water actually have a very little ion (particles that conduct electricity) content due to the filtering process, therefore the pH measuring tool is not able to effectively measure the true pH. It is most likely that the water is at pH 7 or below (due to CO2 in air dissolved into the water causing it to be a bit more acidic), however your pH meter will not be able to register the true pH due to the low ion concentration.

When you add baking soda into that water, the ion concentration increase and allows the pH meter to read and show you the true pH. I believe pH meters measure pH by electricial conductivity or similiar mechanisms.

does this make sense?

[leebca]

Well done Vaporize!

This is what I had alluded to in my post #6 above. This is why I suggested a second addition to see what happens to the pH.

[bguile]

Ok, I believe I understand what you're saying but I guess my confusion comes when I begin to reason in my head and ask questions as it pertains to information and experience that I have accumulated thus far. Like:

1. I just purchased an RO/DI unit. After running my first 30G of water, I tested the pH and it read 8.13 (Pinpoint pH, recently calibrated). I did my water changes in my QT's (approx 90%). The next morning the pH read 7.79!! I typically gravity drip the alkalinity component of B-ionic to try to hold pH steady, but that gets hosed up as the drip slows to an eventual stop. I tried using a test kit this morning to measure. It seems to show that the pH is in the 8.0-8.2 range but I'm not too sure as the kit differentiates with slight shades of pinkish/orange. It has me so worried that I'm going to buy some more calibration solution to recalibrate.

2. If the RO water doesnt have enough ions to read a proper pH am I supposed to add baking soda as the pH drops and keep adding until it raises again? I did that briefly this morning in a cup of ro/di water and it appearred to do that very thing in small variation...however, I was not confident in the result as my confidence in the meter is shaky as explained above.

3. Where does that leave the usefulness of digital pH meters? As stated above if my initial reading of the "pure" RO/DI water is 8.13 am I to assume that it is false based on what you explained above? Would it be the same for my next morning reading of 7.79? Readings like that would have the average aquarist compensating for the low pH and if it's really not that low they/we could be raising it beyond healthy levels.

Help sorting these out would be great. Thanks!

[leebca]

1. pH is the logarithmic concentration of the hydrogen ion. The pH meter probe 'measures' this concentration by the use of a conducting salt. If the water is void of any conducting ions, the probe will give an unreliable reading.

So. . .Reading the pH of RO/DI water with a pH meter is unreliable. If you add a pinch of table salt to the RO/DI water you provide conducting ions in the water without altering the pH and now the pH probe will measure reliably.

I would recommend using calibration liquids that come in the sealed pouch. For the aquarist, buying bottles of pH buffered controls is not very useful. Once opened the pH buffered solution begins to be affected by air. The most accurate calibration of pH probes is using a two-point calibration (two solutions) system. Some pH meters are not so engineered however and only use a single-point calibration.

2. Don't measure the pH of your RO/DI. Start off by adding some baking soda to the water. Mix it thoroughly, then do your first measurement. Go from there.

3. Not "false." The best word is "unreliable." Maybe this is a bit obscure but. . .If you tried to use a magnifying glass in the dark and didn't see anything with it, would you blame the lack of light or the magnifying glass? Same here. The probe needs ions. It's how humans built it. Add some salt to the water if you want to measure it's pH. The value of the pH meter to aquarists is outstandingly high.

So how are you validating that the RO/DI water is proper? Using a TDS meter?

[bguile]

Ok. I think this is starting to make a bit more sense now. I do have a dual TDS meter on the RO/DI unit. I'm reading 7ppm in and 0 out.

So if there is salt in the water the reading could be considered reliable provided that the device is properly calibrated? If so, I guess I really need to work on my method of stabilizing pH. The 8.13 I mentioned early I believe was after I mixed my salt. I'm not certain so I'll have to do it again.

I typically purchase the calibration solutions in the sealed pouches. It's a two point calibration meter also.

Thanks for your help with this.