pH being funky??

[Justinkramp]

Hi there,

I have a fully planted 40g tank.
I use RO/DI water with a pH of 6.10 and I recently disconnected my co2 for CRS and obviously the pH went up. Way up. With CO2 it hovered around 6.6 tank pH and now its at 7.5.

How can my pH be this high if I have a tank with 6.1 DI water thats only remineralized with Gh+?

TDS: 120-130
Gh: 5
Kh:2

inert substrate (BD blasting sand)
5 Indian Almond Leaves
dozen+ Elder Cones

 

[ZxC]

How are you measuring pH?

0 kH can cause wild pH swings. I would target 0.5 degrees of kH using a CO3 source (baking soda, KHCO3 etc.) or use a buffering substrate such as ADA aqual soil and you don't have to worry about any kH

CO2 will drive pH down, shutting it off will cause pH to rise, and rather quickly without any kH in the water.

 

[Dallascowboys16]

It definitely wouldn't hurt to raise your KH a little bit as the previous poster pointed out, but it is normal for about a 1 point ph swing to happen when Co2 is on vs when Co2 is off. If you did your first test when your Co2 had been on for a while I am not surprised by the discrepancy in the results at all.