Tap water PH increases when it stands

Hi there guys

I am stumped, when I prep my tap water and let it stand for more then 24 hours the ph increases. Water running directly out the tap is 7.5

I then add the water to my prepping container with a pump and a hearter. I add some seachem prime and let it stand for a day or 2.

I narrowed it down to my plastic dustibin I store my water in. I then went out and bought a bin for double the price used to store food which garantees it does not leach anything into the water but the same thing happens?

Water out the tap: 7.5
Standing for 24 hours: 8.5

Am I missing something :blink1:

 

The piping getting the water to you may be leeching some metals into the water which would drop the pH. Hence the 7.5. Then when it stands, this leaves the water and goes back up. I've heard of this a few times in SA.

 

I noticed it as well. Especially when you aerate the water. I think it is because you are driving CO2 out, replacing it with oxygen. CO2 bring the pH down, hence the increase when you drive it out.

 

2 very good points.... Something to think about!

 

The water supplied out the tap has likely a reasonable CO2 level. Letting it stand for a day or 2 will allow the CO2 in the water to reach equilibrium. Most likely it will lose some CO2, and thus the ph will rise. This is normal and to be expected and is what is happening. No other reasons (metals, etc.) Also, the CO2 is not REPLACED by O2, they both dissolve in water independent of each other.

 

Thanks for pointing it out. I understand better now. They always talk about gaseous exchange, so my mind short circuited to exchange, as in replace. Nearly the same thing tho, just independent! hehe