# CO2 on timer and large pH swings?



## Laith (Sep 4, 2004)

Yesterday I disconnected my solenoid from my pH controller and connected it to a timer to turn CO2 on and off with the lights (actually on about an hour before lights on). I have a KH of 12.5 so set the bubble rate yesterday to give me a pH of 7, so around 43mg/l of CO2.

This morning after the CO2 being off for over 12 hours, the pH monitor is showing a pH of 7.58.

I know that pH variances shouldn't pose a problem but is there a limit? Here we're talking almost 0.6 of a variance. Is this still tolerable?
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## MatPat (Mar 22, 2004)

When does the time shut the ligths off? I run a similar CO2 setup to yours but actually leave my CO2 running for an extra hour after lights off. This gives me a bit more CO2 in the tank after lghts off and gives me a little "buffer" in the pH rise over the night. You do have a longer lights out period than I do and a higher KH (mine is 5.68 dKH) so you probably have more of a pH swing as a result.

I do believe the plants will still be consuming some CO2 and ferts once the lights are switched off. This will cause more CO2 use and higher pH rise. I would think it takes a little time for the plants to ramp down their CO2 and fert consumption. I mean, they don't shut down immediately when the lights go off. This is pure speculation on my part though


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## rrguymon (Jul 22, 2005)

I am a rookie but I have been turrning my co2 off at night. My pH swings .5 or .6 every day based on the CO2. The fish do not seem to mind at all. The plants are growing well. I have been doing this a couple months. 

This is one of those issues where there are two camps out there. Many people say leave the co2 on 24/7 and others say turn it off at night. Both seem to have good results. I chose to turn mine off. While C02 may be cheap. It will be a PITA to get my tank refilled. The gas store is a few miles away.


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## SnakeIce (May 9, 2005)

A CO2 caused swing does not affect the total disolved solids like a normal ph swing would reflect.

It is the changes in osmotic balance that makes the ph changes stressful for fish. CO2 does not change that so there isn't the same stress because of ph change.


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## Laith (Sep 4, 2004)

Great... thanks for the replies.

Initially I had the CO2 come on one hour before lights on in order to build it back up for the plants. That wasn't enough. Now I'm testing having the CO2 come on 3.5 hours before lights on to try to make sure that the CO2 levels are up there by the time the lights come on.


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## shalu (Oct 1, 2004)

I have 0.5-0.7 ph swings in my tank. No problem. My CO2 goes on 2 hours before lights. 

For me, CO2 saving is only a secondary benefit of putting CO2 on timer. Main reason is to prevent fish loss due to equipment malfunction. It is not a matter of if, but a matter of when.


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## plantbrain (Jan 23, 2004)

A FYI:

Natural planted shallow lakes and pond go through a 2-4 full units diurnal changes daily.

pH 6 at 5 am, pH 9-10 at 6pm.

I thought folks liked natural systems?

We add CO2 for the plants. 
Not for the pH, we just use pH to determine CO2 levels.

Plants do not use CO2 at night, so why add it?
The only reason might be convenience(easier to add it to the filter etc).

Regards, 
Tom Barr


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