# PH meter



## Aqua sobriquet (21 Apr 2012)

Are these any good, seem to be a good price.

http://www.easypet247.com/product.php?id_product=39


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## ceg4048 (22 Apr 2012)

Nice price. Seems to be unbranded so that may be why. Shouldn't be any worse than the liquids, and you can compare the readings for a while until you have confidence.

Cheers,


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## dw1305 (22 Apr 2012)

Hi all,
I wouldn't buy it. The main reason is that it can't be calibrated "_Calibration: Manual (pre-calibrated)_", and this means that you have no idea of whether it is working or not. 

These type of meters are fine for very salty, extremely acidic or alkaline solutions, but as soon as you get anywhere near pure H2O, or around pH7, they are worse then useless.

If you really want a pH meter, you need a meter with a silver chloride or calomel reference electrode and pH4 & pH7 buffers. A Hanna one for about a £100 works reasonably well, but still needs some maintenance of the electrode, and setting up before use. 

You can't just dip any pH meter into a tank and get a meaningful reading. <http://www.ukaps.org/forum/viewtopic.php?f=37&t=19401&p=196512&hilit=pH+meter+Darrel#p196512>

I've got a lab full of pH meters (including bench meters costing £1000's of pounds), but I virtually never read the pH of the tank water, it just isn't a very useful measurement without some other water parameters (particularly conductivity and dKH).

You can buy a cheap TDS meter and this will be both accurate and you can use it as a dip meter. This is all I do.

cheers Darrel


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## Aqua sobriquet (22 Apr 2012)

Thanks very much Darrel, most helpful. Do you have any recommendations for a TDS meter?

Something like this maybe:

http://www.theaquariumsolution.com/tds- ... hermometer

Or

http://www.osmotics.co.uk/products/TDS- ... Meter.html


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## dw1305 (23 Apr 2012)

Hi all,
All TDS meters read conductivity, and they are all OK. I'd pay the extra for a 0-1999 microS meter.
I like Hanna as a make, but manufacturer really doesn't matter for conductivity/TDS meters. 

This one is about £45, has automatic temperature compensation and "manual, single point" calibration.
http://www.hannainst.co.uk/product_info.php?cPath=1202_1250&products_id=2578

You can buy calibration fluids for these, or you can make your own from KCl (potassium chloride). 
The usual calibration solution is 0.01M KCl which has a conductivity of 1411 microS at 25oC. 
Conductivity is approximately linear, so you can go where you like from there. 

7.46g of KCl in 1000cm3 H2O = 0.1 Molar sol., 100cm3 of 0.1M KCl in 1000cm3 = 0.01M and 1411microS. 
&
5cm3 of 0.1M in 100cm3 is ~ 755 MicroS etc.

cheers Darrel


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