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Too much co2?


18 Apr 2013
I have been tweaking my co2 injection, and now have a nice greeny/yellow at start of photoperiod.

The problem is that 3hrs or so into the photoperiod the fish are starting to show signs of stress i.e a few are gasping at the surface.

I must state that the co2 switches on at 2hrs before lights on.

Now if I now turn the co2 off it will mean 4hrs with lights on and co2 off.
Would the plants have,and continue to have, enough co2 when the co2 switches off?
(Caveat - I don't run high tech myself).

Why don't you drop your bps a bit? The dropchecker at the start of the photoperiod shows what the tank has saturated to overnight, so you may be able to achieve that with less.
If I drop my bps slightly then the dc at lights on is green and not lime green/yellow....as I do a daily water change of 10% - 15% before co2 comes on, the dc is blue to dark green when the co2 initially comes on.
Each tank is different. My CO2 comes on 3hrs before lights on and goes off 5hrs before lights out. By the time the photoperiod starts my dc is almost lime green by the time it finishes its just starting to turn back to green.It takes a bit of trial and error to optimise...so fiddle with timing as well, not just bps.
Hi Troi,
On the slightly lower bps It was coming on 3hrs before lights on and going off one hour before lights off and was yellow at lights off. I have been tweaking to try and get a greeny/yellow at lights on. I now have it coming on 2hrs before lights on...then 3hrs into the photoperiod I will need the co2 to switch off which will be 4hrs before lights off.
What I am trying to find out is if that 3hr period with lights on and then 4hrs on without co2 will be enough?
How is your tank doing with the co2 going off 5hrs before lights out?

I should mention I am trying to get the best system I can before I start EI dosing (when my kit arrives) this week.
Even a miniscule change in injection rate can bring CO2 down to a level confortable for the fish. As long as the drop checker is on the lighter side of green, you're doing ok.

If this doesn't work, try to create more turbulence at the waters surface, then adjust your CO2 if it has any significant effect.
It works fine. Like I said 5hrs after the CO2 switches off - and at the end of the photoperiod - the dc is only just starting to turn back to green. I only trimmed 6 weeks ago and my tank now looks like a jungle (poor fish have very little swimming space) and I have zero algae.

The quote below from Clive's article http://www.ukaps.org/index.php?page=co2-measurement-using-a-drop-checker pretty much sums up what you should be aiming to achieve.

'It's much more important that your concentration is up to nominal level in the morning when lights first go on. In the afternoon the concentration has maxed out and the plants are on cruise control. Nearing the end of the day you can throttle back but there is still plenty of gas dissolved and the plants are beginning to lower their consumption.'
Mine comes on 3 hours before lights on, and goes off 4 hours before lights off. The plants are still pearling and the drop checker is still green just before lights off.

You could perhaps just monitor your drop checker/fish and set the timer to turn off the co2 when is starting to get too high
Thanks for all your answers. I guess I have not been very articulate in what I wanted to know:oops:. I now know the answers with your help.
It is just that I think I have been leaving my co2 on too long and stressing the fish out.....I will now turn the co2 off earlier and as long as my dc is green at lights off I will be happy and stop stressing and confusing myself.;) Thanks all.