Been having a few issues trying to get an accurate pH profile so I'll try and make this as clear as possible...
I have a cheap pH pen from eBay. From what I can tell, it works extremely well. My reason for saying this is that, even after 3 months of sitting unused and dry, it still gets the pH reading perfect when I put it into buffer solution. I put it into buffer solution 7, and the pH pen reads 7 or 7.1. I put it into buffer solution 4, and the pen reads pH 4 or 4.1. So it clearly holds its calibration.
However when I tested the tank water with it this morning, it read 6.6. I find this hard to believe. The reason being that when I tested it, the Co2 had been off for 15 hours, and there is enough surface agitation to drive off any residual Co2 during that time. The KH of the tank water is 2.2. Based on the KH of 2.2, a pH of 6.6 would mean a Co2 concentration of around 17-20 PPM. That clearly isn't right, considering all the Co2 should have gassed off during the night. The concentration should definitely be below 10, meaning a pH of at least 6.8 or 6.9.
Secondly, I have taken pH profiles in the past with this pen. According to the pen, my pH took about 7 hours to drop from 7.2 to 6.4. That is clearly awful. However, the fish started to suffer at the end of the photoperiod, so I was left with no choice but to reduce the Co2 injection, and accept an absolutely terrible pH profile, with what I assume to be poor Co2 dissolution.
Now I'm starting to think that maybe the pH profile is bogus, and the pen is inaccurate.
So I suppose my question is this: is it possible that the pen is giving incorrect readings in the tank, despite the fact that it is extremely accurate at measuring the pH 4 and pH 7 buffer solutions? Will the pH 4 buffer solution have a higher KH than the tank? Is the pen unable to accurately measure pH of water with such low KH?
Or is it just that my pH really is 6.6? And if so, why is the Co2 concentration so high after a night of no Co2 and moderate surface agitation?
If the pen is giving me correct readings, then I have a serious problem with my Co2 injection, because I can't even achieve a full pH drop after 7 hours of injection.
If the pen is unable to accurately measure pH in such soft water, would a more expensive pen like this one be able to give me accurate and reliable pH readings?
I hope this all makes sense and I'm very grateful for any responses.[DOUBLEPOST=1407329293][/DOUBLEPOST]Also, let's say my pH is really 6.6. If I wanted to achieve a full pH drop before lights on, that would put the Co2 concentration well above 100 PPM.
I've never really understood this "full pH drop" gospel. In most tanks with a KH above 2, a full pH drop would put the Co2 well above 50 PPM and into lethal amounts. So why do we aim to have a full pH drop when that means having lethal doses of Co2?
I have a cheap pH pen from eBay. From what I can tell, it works extremely well. My reason for saying this is that, even after 3 months of sitting unused and dry, it still gets the pH reading perfect when I put it into buffer solution. I put it into buffer solution 7, and the pH pen reads 7 or 7.1. I put it into buffer solution 4, and the pen reads pH 4 or 4.1. So it clearly holds its calibration.
However when I tested the tank water with it this morning, it read 6.6. I find this hard to believe. The reason being that when I tested it, the Co2 had been off for 15 hours, and there is enough surface agitation to drive off any residual Co2 during that time. The KH of the tank water is 2.2. Based on the KH of 2.2, a pH of 6.6 would mean a Co2 concentration of around 17-20 PPM. That clearly isn't right, considering all the Co2 should have gassed off during the night. The concentration should definitely be below 10, meaning a pH of at least 6.8 or 6.9.
Secondly, I have taken pH profiles in the past with this pen. According to the pen, my pH took about 7 hours to drop from 7.2 to 6.4. That is clearly awful. However, the fish started to suffer at the end of the photoperiod, so I was left with no choice but to reduce the Co2 injection, and accept an absolutely terrible pH profile, with what I assume to be poor Co2 dissolution.
Now I'm starting to think that maybe the pH profile is bogus, and the pen is inaccurate.
So I suppose my question is this: is it possible that the pen is giving incorrect readings in the tank, despite the fact that it is extremely accurate at measuring the pH 4 and pH 7 buffer solutions? Will the pH 4 buffer solution have a higher KH than the tank? Is the pen unable to accurately measure pH of water with such low KH?
Or is it just that my pH really is 6.6? And if so, why is the Co2 concentration so high after a night of no Co2 and moderate surface agitation?
If the pen is giving me correct readings, then I have a serious problem with my Co2 injection, because I can't even achieve a full pH drop after 7 hours of injection.
If the pen is unable to accurately measure pH in such soft water, would a more expensive pen like this one be able to give me accurate and reliable pH readings?
I hope this all makes sense and I'm very grateful for any responses.[DOUBLEPOST=1407329293][/DOUBLEPOST]Also, let's say my pH is really 6.6. If I wanted to achieve a full pH drop before lights on, that would put the Co2 concentration well above 100 PPM.
I've never really understood this "full pH drop" gospel. In most tanks with a KH above 2, a full pH drop would put the Co2 well above 50 PPM and into lethal amounts. So why do we aim to have a full pH drop when that means having lethal doses of Co2?
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