# controling co2 & ph levels in a small tank (7 gal)



## bopper20 (Mar 14, 2005)

hi folks, my specs are below.

my diy co2 - which I added a few days ago (2 liter bottle w/ yeast/sugar, tube going into tank) seems to lower the ph a lot.
it was hovering around 7 before, now it looks like 6.4, 6.5 (hard to tell). I've adjusted it a few times w/ water changes & the chemical that comes w/ the ph testing kit.
but *(here's the actual question)*

IS THERE A WAY TO CONTROL OR STABALIZE PH IN A SMALL TANK

or, actually in MY small tank. I want to get enough co2 in there to help the plants, but don't want to hurt the fish (I guess that goes without saying), but there, i've said it.

thanx man,
bopper20


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## Edward (May 25, 2004)

Hi bopper20

Two questions;
- what is the chemical you use
- what is your KH

Edward


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## bopper20 (Mar 14, 2005)

hi, its from 'aquarium pharmaceuticals inc. it doesn't say what the ingrediant is, just 'ph up'

I don't know what my kh is - I guess I have to get a test kit for that.
bopper


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## bopper20 (Mar 14, 2005)

*anybody?*

any ideas folks?
thanx


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## titan97 (Feb 14, 2005)

To keep your pH stable (especially with CO2 injection), you will need to add some buffer to your water. KH (or alkalinity) is a measure of the buffering capacity of your water. Get a KH test kit and check your levels. You can increase your KH by adding NaHCO3 (sodium bicarbonate aka baking soda). Most people recommend a KH of around 3-5. I run mine higher, but I like very stable water.

-Dustin


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## Bert H (Mar 2, 2004)

> To keep your pH stable (especially with CO2 injection), you will need to add some buffer to your water


Be careful what you add here in the form of 'buffer'. A lot of buffers sold for aquarium use are going to invalidate your kh/co2 relationship. KH is a measure of the 'carbonate hardness' of your water and will play a role in pH stability when you add CO2 because of the equilibrium between carbonic acid/carbon dioxide/carbonate. As long as your KH is 3 or better, you shouldn't have any issues with pH problems if you're injecting CO2. With pressurized injection you simply control the bubble rate to achieve a desired pH. With diy, you don't have that control. If your kh is so low as to not be useable for CO2 injection, you can increase kh by various means (do a search here). Or in small tanks, it might just be easier to use Excel.


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## titan97 (Feb 14, 2005)

You are right about different buffers and the KH/pH/CO2 relationship. The formula to figure out the CO2 concentration from the KH and pH assumes that all of the buffering capacity comes from the bicarbonate/carbonate/CO2 equilibrium. Adding any other buffers in even small quantities can and will throw this relationship out the window. 

I was just using the word "buffer" as a general rule. I'm a chemist, and I tend to speak in very general terms in order to educate other non-chemists. I probably shouldn't have, but I assumed that when we aquarists need more buffer (ie higher KH), we always use some sort of bicarbonate/carbonate based compound.
With that being said, stay away from any and all pH altering chemicals other than bicarbs/carbs if you want to be able to calculate your CO2 concentration. "pH Up" should never be used. Well, I've never heard of a good reason to use it, so I shouldn't say "never".

-Dustin


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## owengibson (Apr 21, 2005)

I think pH up products are more for use with african cichlids and such, not for plants fir the reasons you guys stated.


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## gpodio (Feb 4, 2004)

The best way I've found to control the levels with DIY CO2 is to adjust the depth of the air stone (if you're using an airstone as a diffuser) and also adjust the amount of surface agitation. Knowing your KH is vital as this will allow you to calculate the CO2 concentration, if KH is lower than 3 then you may want to raise it with a little baking soda. I would not try to use any other kind of buffer unless you know exactly what the contents is.

If the PH 6.4-6.5 was stable while using the CO2 setup then perhaps you don't have a problem at all, it's normal to see a drop in PH as the CO2 level goes up, knowing the KH of your water will determine if the concentration of CO2 was indeed too high or not.

I also usually use a smaller bottle for such small tanks as less CO2 is needed.

Not sure if this can help any:
http://www.gpodio.com/diy_co2.asp

Giancarlo Podio


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