Oxygenation And Ph

[Wishful]

Hi
When we had pH problems in our new setup where we were seeing a rise from 6.8 to 7.6 on the RO water we were putting in. I asked some questions on this forum about what might be causing it, but in the end discovered from Eheim (whose filter we are using) that the rise in pH was probably because the spray bar was above the water rather than under it.
We duly moved the spray bar under water and the next water change did not show a subsequent rise in pH. However, after a few days the surface of the water got rather scummy because it wasn't moving at all, so we decided to put an airstone in. This got rid of the scum, but a pH test yesterday showed that, with bubbles in the water, we now have a pH of 7.8!
Can anyone help me understand why oxygenating the water should cause the pH rise? Is there anyway to stop it happening. How are you supposed to oxygenate water in a tank where the pH level it critical?

Thanks for any advice

 

[andywg]

Oxygenating water prevents a build up of carbon dioxide which can cause pH to drop. It should not cause the pH to rise.

I would look at what else is in the tank that may be affecting the pH.

Are you using pure RO water? If so this is likely the root of your problems as the lack of buffering ability can cause wild pH swings in RO water.

 

[Wishful]

Oxygenating water prevents a build up of carbon dioxide which can cause pH to drop. It should not cause the pH to rise.

I would look at what else is in the tank that may be affecting the pH.

Are you using pure RO water? If so this is likely the root of your problems as the lack of buffering ability can cause wild pH swings in RO water.

Thanks for the reply..

We are using pure RO water, but we remineralise it which we understood puts the buffers back in.

What you say is very interesting - the pH rose from the start with just sand and gravel in there. After the lady at Eheim said that the spray bar being out of the water and we submersed it and did a water change, the pH did not rise at all. With the exception of two fish, nothing else has gone into the tank at all but since we put an air pump and airstone into the tank, the pH has risen again.

I'm really confused if oxygenation should be lowering the pH.

 

[CFC]

Aerating the water drives CO2 out of the water, when present the CO2 acidifies the water giving a low pH but when driven out the pH will rise to whatever level the calcium and magnesium levels present there push it to.

 

[Wishful]

Aerating the water drives CO2 out of the water, when present the CO2 acidifies the water giving a low pH but when driven out the pH will rise to whatever level the calcium and magnesium levels present there push it to.

Thanks CFC
So how does one aerate the water well without the pH rising, or is simply that tanks that require a low pH shouldn't have bubbles going through the water?

 

[@ombomb]

You just need to make sure there is surface agitation.

Think ripples on a lake rather than bubbles in a jaccuzi

I have my spray bar so that the water coming through the holes is the exact same level or ever so slightly below the water line, which seems to work well for me.

Out of interest, what in your tank require the ph to be at a certain level?

 

[Wishful]

You just need to make sure there is surface agitation.

Think ripples on a lake rather than bubbles in a jaccuzi

I have my spray bar so that the water coming through the holes is the exact same level or ever so slightly below the water line, which seems to work well for me.

Out of interest, what in your tank require the ph to be at a certain level?

That explains it very well - thank you.

It's not so much for the big tank but the smaller one - I raised the query with the larger tank because there had been a very clear progression of events. We put a spray bar in the smaller tank a little while ago and the pH has gone up a bit in there too, although the spray bar is nearer the surface in there and isn't very strong. We're planning to stock that up with tetra and perhaps a couple of the hardier Rams so we will need the lower pH for them.

Thanks to all for the help on this - I think I understand now.


**Having said that - we want to put Kuhli Loaches in to stir the sand up and I've just read that they prefer water on the softer side so it is relevant after all!