# What do the ph buffer solutions go up to?



## •Cai• (18 Dec 2015)

Hi all, I'm busy cycling my tank and have started to use a ph pen for a close reading on water whilst injecting co2. What id like to know is what do the buffer solutions go up. For example. I have a buffer solution 7.0. Will that read only to a ph of 7.0 and no lower. I've also a buffer 4.0. Again will that read up to 7.0 and no higher?
When I calibrated my ph pen I calibrated with 7.0 and also 4.0 but now I'm not sure wether it's working together or if I have to use one buffer solution until it hits it's limit and then have to calibrate it to other for a lower reading. Sorry if this doesn't make much sense as I'm trying to fathom things out myself. Nothing I can see on their website that helps any.
I should add the ph pen is the essentials hydroponic pen with the ph buffer 4.0 and ph buffer 7.0. They say they work in conjuncture with each other.


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## ian_m (18 Dec 2015)

The solutions are for verifying/calibrating your pen, which due to nature of pH pens needs to be done regularly.

If you pen is fine, putting in pH 7 solution will read 7 and guess what in pH 4 will read 4. Putting it in tank water should also read correct pH.

If pen is out of calibration, you put in pH 7 solution and calibrate the pen until it reads 7. You then repeat, dipping in pH 4 and set the pen to read pH 4. Different pens have different ways of setting the two points, some have two buttons, set 7, set 4, some have an adjustment wheel to set 7 and another to set 4, depends on model of pen. Once set, should read tank water pH correctly.


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## dw1305 (18 Dec 2015)

Hi all,
The pH4 and pH7 buffers are usually used to calibrate your pH pen, by <"2 point calibration">.  You put the pen in the pH4 buffer, and then you press the calibrate button, the meter should then read "pH4", you then give the probe a quick rinse (ideally in RO) and put in the pH7 buffer, press calibrate again and it will read pH7.  The meter is then ready to use.

Cheaper meters have "single point calibration", where you choose the buffer that is at the pH nearest to the solution you want to test (so probably the pH7 buffer), and then press calibrate. It should then be ready to use.

The buffers are <"just solutions"> which will retain their given pH value.

cheers Darrel


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## zozo (18 Dec 2015)

I guess all there is to say probably is writen in Darrels links.. I didn't read it..  But in 2 point calabration you always have to calibrate the valua you aim for as last. For example if you aim for pH 6.5 and calibrate with pH4 and Ph7 buffer. You should first calibrate on pH4 and last on pH7 because your aim value is pH6.5 and is closest to pH7.
So you calabrated 0.5 units away from your aim, the tolerance every meter has is smallest.

Or other way around it all depends on what value your aim is.

If you would calibrate last at pH4 with an pH6.5 aim, you would be 2,5 units away from your aim and the tolerance will be highest.. This accuraty tolerance is probably described in the specs of the datasheet. 

Actualy if you never plan or need to measure near pH4, a 2 point calibration with buffer pH4  doesn't make much sence.. So it's not realy necessary..


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## •Cai• (18 Dec 2015)

Thank you for the replies first of all. I apologise if all this seems a little "well dohhh" but I had to ask the question. 
If I calibrate my pen with the 4.0 solution before a check I generally get a lower reading than if I just switch it on and pop it in tank. That's generally everytime I do it. The 7.0 wasn't giving me a lower reading than 7 but 4.0 was. That's the reason for question. My drop checker is limeade, pearling within tank, good flow with injection of 3bps on a 60ltr tank. My ph before any co2 is 7.3 so I was looking for a drop to 6.3. Only gave me 6.7 at lowest value. My water hardness is very high.
My pen was only 35quid so I'm not expecting miracles. I just expected a limit on the solutions like I said previously. I believe it may just be a one point meter and the word "conjuncture" misleaded me to think otherwise. Nothing to state in instructions what it is in correspondence to being 1point or 2point. 
Thanks for your time everybody


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## zozo (18 Dec 2015)

It is a one point calibration pen..  all suppliers also only state one buffer solution to calibrate it. But as said the 2 point calibration only makes sence if you measure acidity in those values. If you never do, like in much of our cases, we are almost always around 7 (Only the special biotope guys not always) than 1 point calibration will be sufficient. But if you do hydroponics or other gardening techniques there are vegies which like to grow around pH 5, if that's the case you should calibrate on pH4 to get the most accurate.

But than still (with the help of UKAPS) i came to read a lot about pH meters and how they work from the technical point of view and found out that this also is only an estimate, you should always look at your fish etc how they do with what you think you have. If all corralates your good to go and a discrepancy of 0.2 units isn't drasticaly changing things, if it would you already would be running significantly on a very dangerous edge to begin with.


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## Andy Thurston (18 Dec 2015)

Hi Cai

it would appear that your meter is single point calibration so just calibrate it with ph 7 buffer


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## •Cai• (18 Dec 2015)

Thank you for the quick and informative answers. Well appreciated.


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