Unexplained pH drop - HELP! - The Planted Tank Forum
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post #1 of 30 (permalink) Old 10-27-2014, 04:14 PM Thread Starter
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Red face Unexplained pH drop - HELP!

This morning when I checked my Apex, I saw that the pH had dropped over night to 5.9. I checked the CO2 and it was off as expected. I took out the probe and put it in ph7 calibration solution and it registered at 7.3, so if anything it doesn't read too low, but too high.

What could have caused the drop over night? All the fish seem to be ok.

Below is a graph for the last few days. I usually start co2 at 6am, get to a ph of 6.2 around 7am, and then fluctuate between 6.2 and 6.3 until 6pm. Over night the aquarium gets back up to 7.2.

The only problem that I'm aware of is that I added about 200ml of Prime on Saturday during a water change instead of the desired 20ml. Most of this prime never hit the main tank, because I saw the problem in the sump and dump most of the water again before switching on the circulation. Could prime cause this?

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post #2 of 30 (permalink) Old 10-27-2014, 04:22 PM
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What are the readings of Kh and Gh ?
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post #3 of 30 (permalink) Old 10-27-2014, 04:23 PM Thread Starter
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both Kh and Gh are very low - below 20. We have very soft water in the Seattle area.
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post #4 of 30 (permalink) Old 10-27-2014, 04:25 PM
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well...20 Kh isnt exactly low or you meant 20ppm?
That could be the reason ...if the Kh is too low a acid drop can occure
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post #5 of 30 (permalink) Old 10-27-2014, 04:30 PM
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Looking at your chart your pH didn't rise as much the day before leading up to the big drop. Did you change a pump location or anything that is not letting the tank degas as much?
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post #6 of 30 (permalink) Old 10-27-2014, 04:47 PM Thread Starter
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I meant 20ppm, not a KH of 20. Sorry.

Didn't change anything in the tank, besides doing a water change on Saturday. Nothing on Sunday, besides adding 5 nerite snails and 5 Otos.

The not recovering so much between Saturday and Sunday is normal after a water change. I add a bit of Magnesium sulfate each morning which increasing the buffering, but right after the water change it's a bit low.
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post #7 of 30 (permalink) Old 10-27-2014, 04:55 PM
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i think low hardness can cause pH to swing drastically...you are swinging between 5.7 and 7.4 pH...not healthy for the fish IMO.
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post #8 of 30 (permalink) Old 10-27-2014, 04:57 PM
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Smile KH Not GH

Hi,

Magnesium sulfate (Epsom salt?) will not increase the “buffering.”

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post #9 of 30 (permalink) Old 10-27-2014, 05:02 PM
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The KH is the PH buffer a low KH can result in a PH drop or crash or whatever you want to call it. Raising the KH will make the PH more resistant to change. If your running CO2 you want a KH of at least 3dkh. I like using baking soda for raising the KH/PH its the cheapest way.


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post #10 of 30 (permalink) Old 10-27-2014, 05:09 PM Thread Starter
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there's no co2 flowing in right now. Only water circulating from tank to sump and back. It worked like this for 1 months, each night the pH going back up to 7.2, during the day dropping to 6.2 (due to CO2).

I don't understand what could cause the pH to drop over night, when no CO2 is added.
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post #11 of 30 (permalink) Old 10-27-2014, 05:15 PM
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Quote:
Originally Posted by Paul.Gitter View Post
there's no co2 flowing in right now. Only water circulating from tank to sump and back. It worked like this for 1 months, each night the pH going back up to 7.2, during the day dropping to 6.2 (due to CO2).

I don't understand what could cause the pH to drop over night, when no CO2 is added.
When the lights are off, your plants are actually taking in oxygen and putting off CO2. Its not uncommon for PH to drop at night.


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Last edited by greaser84; 10-27-2014 at 05:32 PM. Reason: add
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post #12 of 30 (permalink) Old 10-27-2014, 05:18 PM
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First, even with your regular setup with CO2 turned on during the day and off at night, you are fluctuating between pH a lot during day and night, this is not good.

i guess you need more carbonate buffer to cancel CO2's impact on pH during the day.

Due to low buffer, CO2 being acidic in nature, drops your pH during the day.
At night with no CO2, pH increases.

I would look into increasing the carbnate buffer enough so that CO2 does not impact pH during the day. Target atleast 4dKH.

as suggested above add NaHCO3 (Baking Soda) to increase the buffer to stabilize your pH.



As for why pH dropped overnight, you are running too low of a buffer, any minor change can cause the pH to drop drastically...it would be hard to pinpoint what caused it to drop.

Last edited by rrattani; 10-27-2014 at 07:48 PM. Reason: modified
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post #13 of 30 (permalink) Old 10-27-2014, 07:36 PM
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Smile KH, pH, GH, The Bermuda Triangle of Planted Tanks

Hi,

KH (carbonate hardness) buffers against pH drops (is an antacid) except for CO2 (actually carbonic acid) induced pH drops. Confuses everybody, donít worry about it.

It would appear something in your system is consuming KH.

Have you checked your aquarium KH since you noticed this?

If this were a result of something, you (accidentally) added a couple major water changes should return the system to where it was.

Baking soda, NaHCO3, will raise carbonate hardness adding a small amount (I do not know your tank size) will raise KH, if that stabilizes pH, then you have or had an excess of acid, your system is suffering from acid indigestion. The most common internal source is organic decay.

Another clarification that confuses everyone is that both GH and KH are reported as Calcium carbonate that is an equivalent.

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post #14 of 30 (permalink) Old 10-27-2014, 07:40 PM Thread Starter
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Just tested the water again: KH is 1.5 (22ppm), and GH is 3 or 4.

I added 1 tablespoon of Baking Soda, which raised the pH to 7.4.

I will do a water change now.
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post #15 of 30 (permalink) Old 10-27-2014, 08:04 PM
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Is it better to raise PH, GH & KH using sodium bicarbonate (baking soda) or calcium carbonate?
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