Electronics are not reliable unless they can be tested. My probe always reads high for ph 7 and 10, and therefore calibrates low to compensate. I don't trust it. If Apex temp probe is accurate only to + - 2 or 3 degrees, why should I trust there PH probe? Actually it's not the probe that I question but the transmitter. For the most part, it doesn't matter what the PH is as long as it is stable and in a range from 7.8 to 8.5, correct? Making it read around 8.2 to 8.3 makes me feel better. I'm just being honest (maybe stupid) here.
Low PH....miffed?
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Randy Holmes-Farley
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I don't understand what you are saying about the probe calibrating low, but I understand you don't trust it and some folks do have issues with it. 
Thank you for your reply. When calibrating Apex PH there is a reading that stabilizes for whatever PH solution is used. My readings are alway around +740 for 7 PH nad +1040 for 10 PH. According to BRS this is O.K., and I think according to Apex instructions as well. But, if 700 is actual & PH and 1000 is actual 10 PH., then the readings are 40 or .4 high. I believe the calibration program through some formula, deducts .4 from it's actual reading. If this is correct then A reading of 8.2 would be calibrated to 7.8. A difference of .4 PH.
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I hope it doesn't work that way. Normal pH meters certainly do not, but maybe they oversimplified the description of the calibration process to "make it easier to understand". lol
A pH 7 standard needs to read pH 7, and if it doesn't, that's a problem (assuming they are at the right temperature).
Have you measured the calibration solutions after calibration?
A pH 7 standard needs to read pH 7, and if it doesn't, that's a problem (assuming they are at the right temperature).
Have you measured the calibration solutions after calibration?
Randy Holmes-Farley
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Why would you assume (or even consider it likely) that if it reads pH 7 and 10 solutions correctly, that it isn't reading the tank water correctly? That's the fundamental way pH meters work and are calibrated, even by chemical oceanographers working in seawater.
They do need to be at the tank water temp, or the system needs to know the temp of calibration to correct.
Well, we are going around in circles now. You are the chemist. You tell me. Can I have a DKH of over 15 and low PH at the same time. That and the test kit are what got me thinking., If you say yest then I will go and calibrate my probe again.
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Absolutely many people have normal to high alkalinity and low pH. It is because of excess CO2 in your home air.
It's hard with a system bound pH meter, but this aeration test shows how to diagnose it:
pH And The Reef Aquarium
http://www.reefedition.com/ph-and-the-reef-aquarium/
The Aeration Test
Some of the possible causes of low pH listed above require an effort to diagnose. Problems 3 and 4 are quite common, and here is a way to distinguish them. Remove a cup of tank water and measure its pH. Then aerate it for an hour with an airstone using outside air. Its pH should rise if it is unusually low for the measured alkalinity (Figure 2). Then repeat the same experiment on a new cup of water using inside air. If its pH also rises, then the aquarium’s pH will rise simply with more aeration because it is only the aquarium that contains excess carbon dioxide. If the pH does not rise in the cup (or rises very little) when aerating with indoor air, then that air likely contains excess CO2, and more aeration with that same air will not solve the low pH problem (although aeration with fresher air should). Be careful implementing this test if the outside aeration test results in a large temperature change (more than 5°C or 10°F), because such changes alone impact pH measurements.
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That said, there could be a problem with the pH measurement somehow.
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O. K. The first thing I did was recalibrate my PH probe and retest at 7 and 10. 7 read 6.9 and 10 read 9.9. Close enough. The tank reads 7.98 and after 5 minutes of aeration outside, it still read 7.89 PH. The tank temp is 77.5. Outside 80 degrees. I pumped out side air with air pump and hose into sample foe 5 minutes. My DKH is presently 11.2 and 4 meq. I guess I will just leave things the way they are and assume they are normal. I have done lots of water changes and it seems to make no difference.
I compared my PH readings from apex probe to a salifert PH test kit just out of curiosity and they match. PH is still low...started dosing 2 Part with dosing pump instead of manually adding in the evening. I am dosing 12x/day starting at 7pm to see if this will stabilize the wide swing I am seeing. Will update this post in a few days once some data is gathered. In the meantime...I'm open to suggestions.
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Water changes are useful for dealing with pH issues, except in emergency overdose situations.
Did it really drop using outside air, or is that a typo?
If the pH is really effectively measuring 8.08 with outside air, that's about normal.
ocsurferdad
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Like James said the swing has to do with the CO2 change at night when the lights are off. This happens in the ocean as well but the swing is much less. I started to run my fuge light at night and now the swing is not as bad.
ocsurferdad
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Alk already 230ppm
