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I recently purchased a digital pH meter and I have discovered that the pH in my tank is going through a significant daily fluctuation. In the morning, my pH starts out at around 7.45 and increases to 7.9 within four or five hours. I can't imagine this is good for my fish. My 29g tank is fairly heavily planted, so my guess is that the plants are sucking up all the CO2 in the water in those few hours causing the fluctuation.

My question is is this variance a serious problem? I was thinking of investing in CO2 injection to control the variance.

Hi,
Actually, it is normal for the pH to shift upward when
the lights come on and things start happening in the tank.

No, I don't think that you will have a problem with the
fish because of it.

I'm using bottled CO2 injection and the tank starts off
around 6.6 and climbs to 6.8 toward the end of the 10 hour
photo period. I'm holding at about 30mg/l CO2 saturation.

Adding CO2 injection to hold the pH steady is not really
the reason for all that expense. CO2 injection is added
to furnish the Carbon in and easily used form, for
increased plant growth. Depending upon your KH values,
you add CO2 to reach the desired saturation, and then
leave the settings alone. The tank will normally shift
up and down, slightly.

The lights come on, plants shift to using CO2, you
feed the fish and they eliminate waste products, the
bacteria increase their activity, etc. It's a normal
cycle. The amount of shift will depend upon the
buffering ability of the tanks water, it's KH reading.
The higher the KH, the smaller the shift. Tanks with
CO2 injection are generally run with a KH of at least
3 and generally a tad higher a "5" at most.
KH can be increased by adding small amounts of Baking
Soda to the water. Products such as Arm & Hammer
plain baking soda (no additives) work like a charm and
do not affect the other water parameters.

Frank

-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

renoharps,

What kind of lighting do you have?


My Scapes

You have observed a diurnal fluctuation that will occur in all natural waters. These fluctuations are increased by the relatively high concentration of plants and small volume of water in an aquarium.

pH fluctuations will still occur if you add CO2. You can minimize the fluctuation intensity by adding a controller to the CO2 system. In most cases both the fish and plants are accustomed to the fluctuation. My reading indicates that a diurnal fluctuation of greater than 1 pH may cause fish health problems.

__________
"To steal ideas from one person is plagiarism; to steal from many is research."
researched from Steven Wright

Bob I don't think he is currently adding co2.

Actually my ph actually drops slighly during the day with the addition of co2 via pressure. At nite I turn off the co2 and the ph shifts slightly higher because no co2 is being produced and there's no uptake by the plants. If I left the co2 on all nite my ph would obviously drop do to all the co2 in the tank and no uptake.

My Scapes

Frank, I have considered bottled CO2 with a controller in the past, but when I did the math for a 29g tank, it would have taken me like 10 years to recoup my investment in the hardware as compared to the Excel which I have been using with success. I was considering the CO2 hardware to replace the Excel, increase plant growth, and control pH. You must be using a pH controller to keep your pH that steady or you have a KH higher than 3-5. My KH is between 4 and 5 and I experience a .4-.5 pH fluctuation with no CO2 injection and a moderately heavy plant load.

Tetra, I have 65W of CF on the 29g, so I think I'm borderline on needing CO2, if that's what you were getting to. BTW, how's the Top Gun regulator and the Milwaukee pH controller working out? I thinking that's what I would still buy if I went that route. Another reason I'm considering bottled CO2 again is the "set it and forget it" convenience, even though I have a small tank.

Last edited by renoharps at 09-Nov-2005 10:50

Well, my first question is if the plants are growing well and you don't have alage issues than forget the co2. Why bother. The only thing you will gain is faster growth which means more maintenance. With the 65w cf light you are in range for adding co2 if you felt you need it. As far as the Top Gun, I like it, although others including Little_Fish have had problems with bubble rates. On your 29g once you purchase the regualator ($80) and the cansister (~$80) the co2 will probably last you a couple of years before you have to spend anymore money and you can use the one cansister for several tanks.

My Scapes

Tetra, correct on your assumptions. The only dumb reason I was considering bottled CO2 again was pH control, but if everyone thinks my fish shouldn't have a problem with the .4 to .5 fluctuation, then I'll stick with the Excel.

Last edited by renoharps at 09-Nov-2005 20:18

Hi,
I am not using a controler. I run CO2 24/7/365 and I hold
my KH steady using baking soda when necessary.
I agree with everyone, including you, that the use of CO2
is not a necessity in a planted tank. I've had aquariums
for decades and this last one I decided that I wanted a
lush green jungle with a few flashes of color (fish)
instead of my traditional fishy community tank.

I ran the tank without CO2 for a couple of years and was
happy with it. Then I ran across an article about CO2 and
plants. After reading it, I tried the DIY route and while
it worked, it soon became a chore to constantly mix, fix
leaks, and watch the mix put out huge amounts of CO2 at
first and then taper off to nothing. Then disassemble,
clean, remix, repair another leak, and so on. I decided
that I liked the look of the plants and their growth rates
with the CO2 and that it was worth the investment.
I purchased two bottles (I use one and keep one filled on
reserve) a regulator, bubble counter, and a reactor.
Now my only expense is refilling a bottle once every
8 months for 9$ and some change.

To anyone who has a planted tank and is considering CO2
injection, I would suggest that they try a DIY system
first, and see if it makes a difference in your tank.
It's kinda like speakers, if you can hear the difference
buy them. If you can see a difference, invest.

Frank


-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

Frank,

I already tried the DIY route and was really frustrated by all the mixing, inconsistent CO2 output, etc. I then discovered Excel, and even though it's not as good as CO2 and it had other potential pitfalls, I decided to use it. I was pleased with the results, and for a 29g tank, it made financial sense to as compared to bottled CO2.

Thanks for the advice.

Frank
What would you do with a KH of 11dH I dont know where to start

Hi,
A KH of 11? That's quite high and usually indicates
hard water, the kind that Rift Lake Cichlids and goldfish
like.

You don't mention what your pH is however, if I were
injecting CO2 into that tank, I would inject it at a rate
that would lower the pH to about 7.0. According to the
charts that would give you a saturation of 30mg/l which
would be great.

Frank


-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--