How to lower pH while kH is 0? - The Planted Tank Forum
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post #1 of 22 (permalink) Old 03-01-2016, 08:28 AM Thread Starter
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Question How to lower pH while kH is 0?

I use RO water and add back mineral for my planted shrimp tank. The kH is 0~1, but pH is 7.8. I need it to be like 6.5. From what I read, pH is lowered by reducing kH/use RO water, but that won't work in my case.

How will I be able to lower pH while kH is already 0?
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post #2 of 22 (permalink) Old 03-01-2016, 10:43 AM
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R/O water should have a pH around 5.5 or so. So adding 5.5 pH R/O should "dilute" your 7.8 pH water, thus lowering it.

Otherwise you can use other acidic sources via active substrates (acidic buffering substrates such as ADA Aqua soil), tannin/humic acid sources like peat moss, Indian Almond Leaves, Alder Cones, Cholla wood, driftwood tannins, etc. I think there are tannic/humic acid tinctures (liquid), and I think I've heard of them in concentrated powder forms as well, though research would need to be done to know how to go about properly/safely using them.


EDIT: Oh I missed the part about it being a shrimp tank. I would assume this is for soft acidic Caridinas, in that case I would definitely recommend a active acidic buffering substrate. It keeps the water stable in the acidic range, which both (acidic water and stability) are crucial to keep Caridinas healthy. I am not all too familiar with what substrates are best for that, but ADA aqua soils are common. Browse them. You can ask for recommendations on The Shrimp Spot forum (tons of experienced help there) and/or do searches for best Caridina shrimp substrates.


With a KH of 0-1 though, and using R/O water, your pH should be a lot lower.
What's your GH?

If you have to, (actually it is really recommended when dealing with shrimp, especially Caridinas), use 100% R/O water and just remineralize.
If you are already, what remineralizer product(s) are you using?
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post #3 of 22 (permalink) Old 03-01-2016, 10:57 AM Thread Starter
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The tank is established over a year, decently planted with driftwood, Fluval Plant and Shrimp Stratum as substrate. It's recently converted to shrimp only tank. I'm already using RO water, remineralize with Seachem Equilibrium, target TDS 150, GH 5.

Quote:
R/O water should have a pH around 5.5 or so
So this got me confused the most. My RODI water has pH = 7.6, TDS 0. Does that mean my water has less CO2 dissolved than normal? AFAIK, the only other factor for pH between kH is CO2. But I don't want to run CO2 if possible...
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post #4 of 22 (permalink) Old 03-01-2016, 12:28 PM
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check your PH test kit.
PH=7.6 happens at like KH=7 TDS=200 or something like that
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post #5 of 22 (permalink) Old 03-01-2016, 01:53 PM
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What happens if you set out some RO water, exposed to the air for 24-48 hours, perhaps run a bubbler or small pump (reaction happens faster- half hour to an hour)?
If it is low in CO2, then it would pick up CO2, and this would lower the pH.

The organic materials listed by WaterLife ought to work, do you know if they are OK with shrimp?

Are you using API kits? The mid range pH test? (not the high range?)
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post #6 of 22 (permalink) Old 03-01-2016, 02:03 PM
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pH is affected by KH and TDS, but they don't directly correlate. My tank runs TDS 100, KH<1, and pH ~7.2 right now (in the evenings). Lots of plants taking up CO2, without being balanced by a large animal respiratory load. Also have a cubic foot of peat in there, FYI.

To consistently drive pH low, you need a consistent acid source. Doesn't matter if your KH is 0 if there's no acid source.
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post #7 of 22 (permalink) Old 03-01-2016, 02:47 PM
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How are you measuring pH? A pH meter is inaccurate in low TDS solutions. Dye solutions (drops) are your best bet.

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post #8 of 22 (permalink) Old 03-01-2016, 03:21 PM
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RODI water can't have pH lower or higher than 7.0. It's completely neutral. Of course when it's fresh it can have some CO2 dissolved, but after airing it, it will go to 7.0, but cause KH=0 bringing pH down is super easy. Just let it sit with some peat and done :-)


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post #9 of 22 (permalink) Old 03-01-2016, 05:11 PM
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I doubt that even RO/DI water has zero KH. That would mean there is absolutely no carbonate/bicarbonate ions in the water, and the RO/DI system works absolutely perfect. We just don't find perfect stuff in real life. So, you very likely have just near zero KH. So, the CO2 dissolving into the water from the air should drop the pH below 7.0. The lowest that CO2 can drop the pH is around 5.5, so that would be why RO/DI water can have a 5.5 pH normally. If you are using a pH test kit to measure the pH, I suggest getting a new one, just in case the reagent in the current one is deteriorated.

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post #10 of 22 (permalink) Old 03-01-2016, 06:53 PM Thread Starter
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Quote:
Originally Posted by KevinC View Post
How are you measuring pH? A pH meter is inaccurate in low TDS solutions. Dye solutions (drops) are your best bet.
Really? Do you have more information about meter vs test solution vs test strip?

I do use pH meter, and actually did a calibration last night to make sure. Never thought low kH would affect its readings.

I don't have any other pH tester around at the moment.
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post #11 of 22 (permalink) Old 03-01-2016, 06:57 PM
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Quote:
Originally Posted by zsxking View Post

So this got me confused the most. My RODI water has pH = 7.6, TDS 0. Does that mean my water has less CO2 dissolved than normal?
How old is the rodi system? might be time for some new filters in there since as others have pointed out you shouldn't be seeing those numbers out of a rodi unit.

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post #12 of 22 (permalink) Old 03-01-2016, 07:03 PM
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What's the pH, GH, KH, TDS of your R/O water before remineralizing with Equilibrium?
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post #13 of 22 (permalink) Old 03-01-2016, 07:49 PM Thread Starter
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Quote:
Originally Posted by WaterLife View Post
What's the pH, GH, KH, TDS of your R/O water before remineralizing with Equilibrium?
7.8, 0, 0, 0

This is the reading from water freshly out from RO/DI unit. Let it sit for an hour, lowest pH it gets is 7.6. All reading from pH meter pen.

RO/DI medium are replaced like 3 months ago.
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post #14 of 22 (permalink) Old 03-01-2016, 09:12 PM Thread Starter
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Just went to LFS to test the water's pH with API test kit, got 7.6, same as the reading from pH meter. So the meter should be accurate.

Also got some indian almond leaves, see if it helps.
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post #15 of 22 (permalink) Old 03-01-2016, 11:28 PM
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Here's a technical note about pH meters in low TDS: Measuring the pH of Pure Water from Cole-Parmer

Since the LFS agrees, then that removes that possibility. I'd look for a contaminant - even the tiniest amount of contamination could raise the pH since there is nothing to counteract it (no kH). A tiny bit of calcium carbonate residue anywhere in the storage tank or the presence of old snail shells in the tank could do it.

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