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pH changes

Julian

Julian

Member
Joined
20 Jul 2013
Messages
688
I like to think I have a fair amount of knowledge when it comes to CO2/pH but something is confusing me.

Using a calibrated pH pen, I've measured the water inside the tank after turning off the CO2 for 2 days and it measured 7.5.

Using the same pen, I measured a sample of water taken from the tank and left in a bowl for another 2 days, this gave me a reading of 8.5.

I don't understand why the pH increases to 8.5 when I take the water out of the tank.

I understand rocks and substrate can alter pH, but I would have thought that even if I remove a sample of water away from the rocks and substrate, the pH would still be the same?
 
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Temperature can have influence (you'll see calibrating fluids are usualy valued at 20 degrees celcius), water movement at the surface (in the tank) can facilitate more CO2 in the water (lower pH), precipitation of minerals because the liquid has cooled.Just things that can happen. I think escaping CO2 is the most propable.
 
pH pens are notorious for being affected by other salts in the solution as well as electrical interference.

Really you should only measure tank water samples within a couple of hours of each other and in same sample areas ie in tank or out of tank or else as you have found pH readings can be very different.

If you are measuring water taken out of the tank, compared to water in the tank, you should really disconnect all electrics (off and unplugged) before taking the tank reading. Many people have been confused by the pH in the tank being different to exactly the same water taken from the tank and measured in a cup. Due to electrical interference some people have reported of seeing a pH difference of over one unit pH between opposite ends of the tank. !!!!

When measuring pH drop due to CO2 as your samples are within an hour or two and hopefully under similar conditions, you should be OK.
 
Thanks guys. So is it safe to say that I should still be aiming for 6.5 at lights on?

Sent from my Nexus 5 using Tapatalk
 
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