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Old 07-24-2007, 02:18 PM   #1
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newly pressurized and ph swings

Hello all,
I got my CO2 up and running complete with PH controller.

I set it up according to the instructions and it seems to be working fine, but the pH keeps going up and down. I have the controller set at 7.0 (my KH is 8 ) and watching the pH meter it goes up and down +/- between 6.9 and 7.3.

Before bed last night it was right around 7.0 when I turned the lights off. Nothing is on a timer so I didn't turn anything off but the lights.

But when I got up this morning the pH was at 8.3; the flow seemed to have stopped entirely (no bubbles in the bubble counter) even though the alarm light was blinking on the controller. So I adjusted the flow control knob on the regulator until bubbles were coming again and it began correcting itself. (I am not entirely convinced that my son didn't tweak the knob when he got up early this morning...he says no, but he is only 4....I have since locked the cabinet up so no one can mess with it.)

I am just wondering how much of a fluctuation is normal? Obviously there will be adjustments in the beginning but in a couple weeks when I put fish in I am worried that the fluctuations will cause stress.

Anyone have experience to offer?

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Old 07-24-2007, 02:43 PM   #2
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When you start a new tank of CO2 - often times it does this trailing off pressure thing, where you set the pressure right, but over the first day or so it slows to a crawl or stops. Best way to avoid it IME is to set your low pressure side up to about 30psi if your regulator lets you control that (I use Milwaukees). Otherwise just anticipate this and tweak with it for the first day or so. After that it should stabalize.

You also need to calibrate your pH meter for first use. Basically dip the probe in the bag of 7.01 reference solution and adjust the meter to 7.0 with the little blue screw driver (assuming an SMS122). I would recommend leaving it soak in the reference solution for 3-5 minutes, then calibrate, rinse and put back in the tank.

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Old 07-24-2007, 03:48 PM   #3
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OK, good to know. I did calibrate the pH meter before first using it.
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Old 07-24-2007, 04:12 PM   #4
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Exactly as said, it'll take a bit before the needle valve gets adjusted to where you want it. The reg breaking in, pressure relief, etc. I've found it actually takes several days for me to get everything adjusted properly, but once you do it should be good to go.

I would recommend turning your CO2 off at night as well, not just the lights. With no light, the plants are not generating O2, and you could possibly not maintain enough O2 for your inhabitants when this happens. Also, since plants aren't using the CO2, it's just going to waste. Turning it off at night can double the amount of time you get out of your tank.
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Old 07-24-2007, 04:22 PM   #5
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But if I turn the CO2 off at night, wouldn't it cause my pH to go back up to 8.2 (where it was before starting the CO2 injection) and if so wouldn't that cause the fish to stress?

This issue is of particular importance to me as I am planning to eventually have discus in this tank but want it to be fairly stable.
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Old 07-24-2007, 04:45 PM   #6
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Having pH changes due to CO2 has not been known to cause problems with fish. Having pH changes due to KH changes can be very stressful to fish.

Since you are running a fully automatic system, there is no need to turn off the CO2. Having CO2 in the water column does NOT displace O2.
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Old 07-24-2007, 04:53 PM   #7
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It's a common misconception that changes in pH will stress fish, because most of the time KH and pH will shift at the same time. More people have pH test kits so people look at the pH instead of KH when looking for stability. However when you start injecting CO2 you have to throw out this misconception. It's the changes in KH that actually stress the fish and also causes the shift in pH. When pH changes solely due to CO2 injection, it will not stress your fish.

That being said you can inject too much CO2, which would hurt your fish. Generally you have to inject over 100ppm for this to happen and you would see your fish swimming at the top of the tank gasping.

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