# Fluctuating CO2 causes algae?



## Uncle Rico (Oct 22, 2007)

I recently got a CO2 system with a solenoid. Right now it is running so that the CO2 shuts off at night. I noticed that the PH rises from 6.8 to 7.6 overnight, indicating that the CO2 levels are dropping significantly at night. *Will this trigger algae if this happens every night?* Also, is this bad for the fish? I was wondering if it would be better to just leave the CO2 on at night so that there is a more stable CO2 level.

*One of the reason I got the regulator is because people say that the unstable CO2 levels using the yeast method will encourage algae. My PH was much more stable when I was using that method since the CO2 would be on 24/7 and my air pump would turn on at night to try and prevent excess CO2 buildup.


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## Error (Apr 16, 2004)

My CO2 is hooked to my light timer and comes on/goes off with the lights. I haven't experienced any algal blooms that I would attribute to the CO2 levels fluctuating. My fish are fine, including cardinal tetras, Pelvicachromis, and some Loricariids. I wouldn't worry about it, particularly if you've already been doing it and haven't seen any ill effects.

Yeast systems have trouble maintaining stable levels of 20+ ppm CO2, which can cause algae. It is very important if you use CO2 that you have adequate amounts during the plants' photoperiod.


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## FobbyBobby23 (Mar 8, 2005)

i think it would be more of fluctuating CO2 during the lighting period that may cause algae


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## niko (Jan 28, 2004)

One of the main things about planted tanks is keeping things stable. That's something that's seldom discussed but tanks that do well usually don't have much fluctuations of any parameters.

To me personally shutting off the CO2 at night is a pretty useless exercise. It doesn't take long for the Co2 to fizz out of the system. But it takes an awful lot of time for the CO2 level to get back to "normal" in the morning. Is that a good or a bad thing is hard to say, but my opinion is that the more stable the parameters the better. So I'd say don't shut off the CO2 at night.

How much CO2 are you really saving but not running it at night? Do you think that your plants will do considerably better by shutting the CO2 at night? Do you think that pumping air at night will make your plants grow like crazy? 

My point is that the simpler/easier you run your tank that better off you and the tank will be.

--Nikolay


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## hoppycalif (Apr 7, 2005)

Assume you keep the lights on for 10 hours, or even 12 hours. Shutting it off at night will then double the time between refills. It isn't the cost that is significant, just the bother. And, if you run the maximum concentration that doesn't threaten the fish, they need a break from it at night. Those are the two reasons for shutting it off at night. But, if you can do well with only 20 ppm or so of CO2 the fish should be able to tolerate it for 24 hours a day, with no problems, and that can be at half the bubble rate as for 30+ ppm, so you still get the extended time between refills. I think it is just a matter of what you prefer.


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## Newt (Apr 1, 2004)

You could do 2 things:
(1) Get more plants as they produce CO2 during the night - cheaper but might not be very effective
(2) Get a pH controller and plug your solenoid into that - more expensive but more reliable, less fluctuation


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