Does turning CO2 on before the lights actually make a difference?

[snowballs99]

Hey guys, I use CO2 misting on all my planted tanks. I never really had much issues with algae or plant issues related to CO2.

I was wondering how many of you actually turn co2 on 2-3 hours before the photoperiod and if it actually made a difference in your tanks.

I wasn't sure if it was worth buying a few extra timers for co2 and light seperately.

 

[Kwyet]

Mine comes on 3 hours before the lights. That keeps CO2 steady within 5 ppm for the daylight hours according to the Hanna test. I do think it makes a difference but I don’t have any hard data for you. @Naturescapes_Rocco has a lot of info in one of his threads though.

 

[Koan]

I use these guys, super easy app control



Over to you, @Naturescapes_Rocco

Resource Thread 'Hanna CO2 Test Kit: My experience so far (and why you're probably not starting CO2 injection early enough)!'

Mar 27, 2025

The 2hrAquarist legend Dennis Wong tested the Hanna Test Kit vs a $3,000+ CO2 testing device and found accurate results in low kH aquasoil based tanks when compared. $30 for CO2 readings vs $3,000+!

It's a simple kit that comes with simple instructions, two differently sized vials for different detection ranges, a titration syringe phenolphthalein indicator, and an NaOH solution of some unknown concentration to titrate with.

For the range of detection on the Hanna CO2 test kit we want (0-50ppm):

• Add 10mL of aquarium water to the small flask. Add 1...

• Naturescapes_Rocco
• co2 co2 measurement hanna injection test kit titration
• Replies: 39
• Forum: Fertilizing and Aquarium Chemistry

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Post in thread 'New Yugang Testing'

Dec 3, 2025

Quick note on pH drop as a tool for CO2:
I've tested extensively in different KH tanks, and find that "pH drop" methods vary as wildly as trying to read a "ppm number" from drop checkers colors. A 1.0pH drop (from degassed) does not equal 30ppm in low KH tanks, or high KH tanks. The range seems to be between 3-6KH for a 1.0pH drop to equal 30ppm CO2. You will need 1.2-1.5 at 0-1KH for ~30ppm CO2, and 0.8pH drop at 6-10KH for 30ppm CO2. For me, it's just not accurate and has too many factors!

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The basics​

What pH readings are most useful for:
Since CO2 injection is...

• Naturescapes_Rocco

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[Naturescapes_Rocco]

Your question was does it actually make a difference, and the answer is yes. I've basically doubled my rates of success with this hobby once I realized having good CO2 when the lights come on really makes a difference.





You don't HAVE to do this to be successful. If your system isn't blasting light during the photoperiod (medium or low strength lights) you can get plenty of success starting CO2 injection 1 or 2 hours beforehand.

If you have super high energy systems and find it difficult to grow certain plants or always get algae, try starting your CO2 way earlier in the day.

 

[DutchMuch]

Your question was does it actually make a difference, and the answer is yes. I've basically doubled my rates of success with this hobby once I realized having good CO2 when the lights come on really makes a difference.

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You don't HAVE to do this to be successful. If your system isn't blasting light during the photoperiod (medium or low strength lights) you can get plenty of success starting CO2 injection 1 or 2 hours beforehand.

If you have super high energy systems and find it difficult to grow certain plants or always get algae, try starting your CO2 way earlier in the day.

Wow thank you Rocco, i had to read this over a few times but eventually understood... i will have to increase the time my Co2 turns on! Thank you!

 

[Naturescapes_Rocco]

Wow thank you Rocco, i had to read this over a few times but eventually understood... i will have to increase the time my Co2 turns on! Thank you!

Glad it was helpful!
If you start injection earlier, make sure to keep an eye throughout the day. I explain it in this post.

If you happen to be injecting like this ^ starting your CO2 even earlier would be fatal.

Ideally, your setup should reach an equilibrium less than 50ppm.
Technically, with a properly dialed CO2 setup, you should be able to inject CO2 24/7 without gassing your fish, like this:

 

[snowballs99]

thanks for the replies guys.

I usually get pearling in the afternoon on my plants, after 3-5 hours of co2 + lights being on.

I'll try to adding co2 3 hours earlier and seeing what the results like.
I'll also turn co2 off 2 hours earlier just to save some gas and save a refill trip.