PH being really low after a week away

Wolf89

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Recently bought a Milwaukee constant PH probe. Set it up and calibrated about a week before I left (for Milwaukee coincidentally). I was happy with the readings, with it getting up to 8.3 during the day and 7.9-8.0 at night. I come back after a week vacation (its been a few days now) and PH is struggling to hit 8.0 and is 7.6 at night. I recalibrated today to ensure that wasn't the problem. The only thing that I know that changed is that the ALK fell to 7.7 from from my normal 8.5-9, which I am slowly raising. I am trying not to chase PH numbers, but I feel that nothing is totally happy and 7.6 is really low.
 
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zheka757

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I don't think its possible to sustain any number below 7.8 without the sand and rocks dissoling and in turn buffering the water (maybe I am wrong?)
i personally had it below 7.8, I have recalibrated my ph meter many times for same reason, and i have had my ph at 7.7 before, but to be fair i also had my alk drop to low 7's at same time.
 

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To have a pH of 7.6 with a 7.7dKH would require a CO2 level of 2300 which is harmful to humans with extended exposure.

SmartSelect_20220630-194342_Pydroid 3.jpg


It's very unlikely that your air quality is that bad...you would definitely notice.

So either your tank has poor aeration, your actively dosing something that lowers pH, or your pH measurement is wrong.

Based on our poor pH accuracy hobby testing kits and probes which are often +/- 0.2...I'd suspect your probe.

You can easily diagnose what the issue is with cup aeration tests.
 
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Wolf89

Wolf89

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To have a pH of 7.6 with a 7.7dKH would require a CO2 level of 2300 which is harmful to humans with extended exposure.

SmartSelect_20220630-194342_Pydroid 3.jpg


It's very unlikely that your air quality is that bad...you would definitely notice.

So either your tank has poor aeration, your actively dosing something that lowers pH, or your pH measurement is wrong.

Based on our poor pH accuracy hobby testing kits and probes which are often +/- 0.2...I'd suspect your probe.

You can easily diagnose what the issue is with cup aeration tests.
You must be right. Just checked it before lights come on... Says 7.4... obviously that can't be right. But what am I supposed to do? Calibrated the probe yesterday, and the probe has only been used for 3 weeks, otherwise brand new.
 
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Wolf89

Wolf89

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After you calibrated, can you now read pH 7 and 10 correctly?
Yes, I just opened a brand new calibration packet and it read 7.0, like it should.
This tank is in a basement (does co2 rise or sink) so I don't think it's impossible for the co2 levels to be so high... But it's especially weird since nothing has changed before I left. The only thing I can think of is the the humidity is a lot higher (don't know %) because the dehumidifier wasn't emptied.
 

Randy Holmes-Farley

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Yes, I just opened a brand new calibration packet and it read 7.0, like it should.
This tank is in a basement (does co2 rise or sink) so I don't think it's impossible for the co2 levels to be so high... But it's especially weird since nothing has changed before I left. The only thing I can think of is the the humidity is a lot higher (don't know %) because the dehumidifier wasn't emptied.

The 7 is not the best test. Tgat does not check the slope of the calibration. Check that it reads the 10 properly.

the calibration fluids may also be off.
 

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i personally had it below 7.8, I have recalibrated my ph meter many times for same reason, and i have had my ph at 7.7 before, but to be fair i also had my alk drop to low 7's at same time.

Couldn't that 7.7 be within the error range of the probe? A lot of pH tests or probes have a +/- 0.1 or 0.2 error range
 
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Wolf89

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The 7 is not the best test. Tgat does not check the slope of the calibration. Check that it reads the 10 properly.

the calibration fluids may also be off.
Sorry for the delay. Just tested, it read 10.0 perfectly. So it read both 7.0 and 10.0 on the dot, so I don't think the monitor could be reading wrong? Is it possible for PH to really go as low as 7.4 at night?? I have no idea what could have caused this to change from the 8.0 at night I used to have. I know not to chase numbers, but 7.4 seems detrimental. Its only 7.9 right now after the lights have been on for 7 hours
 
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Sorry for the delay. Just tested, it read 10.0 perfectly. So it read both 7.0 and 10.0 on the dot, so I don't think the monitor could be reading wrong? Is it possible for PH to really go as low as 7.4 at night?? I have no idea what could have caused this to change from the 8.0 at night I used to have. I know not to chase numbers, but 7.4 seems detrimental. Its only 7.9 right now after the lights have been on for 7 hours
In that case, assuming the Alkalinity is still correct it would appear that you have a CO2 problem.
 
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Sorry for the delay. Just tested, it read 10.0 perfectly. So it read both 7.0 and 10.0 on the dot, so I don't think the monitor could be reading wrong? Is it possible for PH to really go as low as 7.4 at night?? I have no idea what could have caused this to change from the 8.0 at night I used to have. I know not to chase numbers, but 7.4 seems detrimental. Its only 7.9 right now after the lights have been on for 7 hours

Yes it's possible to have very low pH due to:
  1. Poor aeration
  2. High CO2
  3. Dosing
  4. Overstocked Tank
Otherwise, it's usually a measurement error.

Cup aeration tests can help identify what's really going on.

How I use a cup aeration test to help pinpoint certain pH issues.
  1. I do 2 tests. One outside and one next to the tank.
  2. I run an airstone for about 1 hour and measure pH.
  3. If the outdoor test isn't around 8.2 NBS (for my 7.7dKH tank), then I know I have a meter or Alk issue...and it's never an Alk issue.
  4. If the next to tank test is below 8.2 NBS, then I have higher indoor CO2...almost always the case.
  5. If the next to tank test is higher than the tank, I have an aeration issue or something else that is driving down pH...it's almost never something else unless I'm dosing something that lowers pH.
  6. If the next to tank test is lower than the tank but not at desired levels, then I need to look at my pH management setup.
 

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