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How much variance in CO2 levels is ok

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I have read many times that inconsistent CO2 will contribute to algae growth, but I'm not really clear on what inconsistent means in this context. I just set up my first injected CO2 system and I'm having it turn off at night with the lights since the plants won't use much in the dark. I have read many other people do this too. Will that type of on/off cycle result in the inconsistency I read warnings about?
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Discussion Starter · #3 ·
Thanks!

Sounds like I better set up a second timer so that the CO2 comes on before the lights then.

As far as consistency from day-to-day I started at about 1/4 bps and have been slightly increasing it every day until I get to 1.5 bps or so to make the transition easier on the fish. Would I be correct in assuming it's only a decrease in CO2 that's a real problem?
 

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Yeah a sharp decrease is the main thing to worry about, or just up and down levels in general. There's nothing to worry about slowly increasing over a few days to reach an optimum level.

You should definitely get a second timer in order to have the CO2 level up when the lights come on. I have mine set to come on 2 hours before the lights, and go off 1 hour before the lights go out.
 

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It really depends on how sensitive is your fish. I have nano tanks where my drop checker would go yellow within a day, and the fish displayed no signs of distress. But those are tetras, loach, danios, betta... not the most finicky of the fish. My shrimp looked a little disappointed when I added too much CO2 too fast, but were fine the next day.

Either way, it's not the CO2 levels that are a problem (at least until you overdose it so much that your fauna starts to suffocate). What stresses out the fish is the rapid pH swing. pH changes happen in nature all the time over the course of a day (as plants consume carbon and the sunlight varies), so as long as you're not going from 8 to 6 in a couple of hours, your fish should be OK.

as far as algae, I can't really comment; IMO, there are too many factors that contribute to algae growth to reliably tie it to CO2 variance.
 

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It really depends on how sensitive is your fish. I have nano tanks where my drop checker would go yellow within a day, and the fish displayed no signs of distress. But those are tetras, loach, danios, betta... not the most finicky of the fish. My shrimp looked a little disappointed when I added too much CO2 too fast, but were fine the next day.

Either way, it's not the CO2 levels that are a problem (at least until you overdose it so much that your fauna starts to suffocate). What stresses out the fish is the rapid pH swing.
Not true. BBA is by far the worst algae in an aquarium and that almost always starts when the ppm of CO2 in the water is not kept about the same, day to day. When you add CO2 to the water you always get a drop in pH, which does no harm at all, to fish or plants. Rapid changes in KH will probably stress the fish a lot, while also increasing the pH. That is the effect of the KH not the pH.
pH changes happen in nature all the time over the course of a day (as plants consume carbon and the sunlight varies), so as long as you're not going from 8 to 6 in a couple of hours, your fish should be OK.

as far as algae, I can't really comment; IMO, there are too many factors that contribute to algae growth to reliably tie it to CO2 variance.
Algae in general are a bigger problem the more light you use. Using an appropriate level of CO2 in the water allows the plants to grow fast and healthy, which is the best defense against algae. Start with a very clean aquarium setup, use enough CO2 to fill the growth needs of the plants as dictated by the amount of light you have, and you should avoid any algae problems, until the tank and its system start getting too dirty. But, do a good job keeping everything clean and algae should not start growing. But, forget to refill the CO2 bottle for a couple of days, or develop a leak that drops the amount of CO2 in the water for a couple of days, and BBA will very likely start growing very well.
 

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Not true. BBA is by far the worst algae in an aquarium and that almost always starts when the ppm of CO2 in the water is not kept about the same, day to day. When you add CO2 to the water you always get a drop in pH, which does no harm at all, to fish or plants. Rapid changes in KH will probably stress the fish a lot, while also increasing the pH. That is the effect of the KH not the pH.
Algae in general are a bigger problem the more light you use. Using an appropriate level of CO2 in the water allows the plants to grow fast and healthy, which is the best defense against algae. Start with a very clean aquarium setup, use enough CO2 to fill the growth needs of the plants as dictated by the amount of light you have, and you should avoid any algae problems, until the tank and its system start getting too dirty. But, do a good job keeping everything clean and algae should not start growing. But, forget to refill the CO2 bottle for a couple of days, or develop a leak that drops the amount of CO2 in the water for a couple of days, and BBA will very likely start growing very well.
+1
Once @#$% hits the fan BBA will ruin you. I have experienced this firsthand. If you run a good amount of light and CO2 you have to make sure the CO2 is consistent. Mess around with it all the time and BBA will attack you. Also if things get too dirty you will get attacked by algae (probably not just BBA). Algae loves dissolved organics.
 

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@hoppy, @klibs: not in my experience, but then again, there are as many opinions as there are fishkeepers.

Bump: @hoppy, sorry, should clarify: I do certainly agree that algae becomes a problem at higher light levels. I wasn't really commenting on that.

But I have not found CO2 levels variance to stress the fauna.
 

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@hoppy, @klibs: not in my experience, but then again, there are as many opinions as there are fishkeepers.

Bump: @hoppy, sorry, should clarify: I do certainly agree that algae becomes a problem at higher light levels. I wasn't really commenting on that.

But I have not found CO2 levels variance to stress the fauna.
I think you're in agreement with everyone here, and appear to be disagreeing with your earlier post...

If CO2 level variance doesn't cause fish stress, then by necessity pH changes in the absence of KH changes do not cause fish stress.

This is absolutely necessary, as the only way to change pH without affecting KH is to increase or reduce CO2.

Hence the common expression that pH doesn't affect fish, KH does, because CO2 swings don't stress them.
 

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I used DIY CO2 for a couple of years and, even with low light I got BBA consistently. When I switched to Excel/Metricide I was able to use more light, and still did not get BBA. The main characteristic of DIY CO2 is that it is not a constant source of CO2. The level starts low, builds up to a maximum, then slowly drops back down. So, it is virtually impossible to maintain a consistent level of CO2 with DIY CO2 (yeast method), and that made it very difficult for me to avoid BBA. I'm sure there are people who have not had that experience, but I'm equally sure they are the minority.
 

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Discussion Starter · #13 ·
As far as night time gas levels go, I've hear of running an air stone when the lights are out to add oxygen and surface agitation. Judging from what's been said here it doesn't sound like it would be bad for the plants and I'm pretty sure it would be good for the fish. Would there be any reason not to?
 
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