# Large W/Cs and CO2



## abwalker (Feb 25, 2005)

I'm generally a lurker on this site. My tank does wonderfully, but I want to free up my weekends a little and do larger water changes on a bi-weekly basis as opposed to 15% weekly. My question is, how do you change a lot of water in a tank who's pH is controlled by CO2 injection? My water is very soft, so I buffer it up with bicarbonate. It goes from about 7.2 to almost 8 and the CO2 brings it back down to just slightly acidic. I am worried that by doing larger changes, I will subject my fish to a suddenly high pH, followed by a significant decrease in pH. The CO2 is controlled by a Milwaukee controller and regulator/solenoid. I keep the CO2 between 18 and 30ppm. 

3 months ago, I converted my tank (50gal) from a relatively low tech (NO's and yeast CO2) to a brighter, more dynamic lighting setup and pH-controlled pressurized CO2. The tank has a bright side, 150 MH pendant, and a dimmer side with normal output lamps in DIY light boxes that go "the short way" across the tank. The bright light side has stem plant including ludwigia sp., Myriophyllum mattogrossense, Eichhornia diversifolia, dipidis diandra, and Nesaea pedicellata, the dim side has an extremily dense stand of crypt wendtii and balansae and some anubia var. coffeefolia (sp?). The forground is Hemianthus micranthemoides on the bright side and a dwarf sag elsewhere. Fish are gouramis, corys, SAE's, hengel's raboras and 3 clown loaches (for as long as they behave themselves). The tank is 50gal. The substrate is old. Very old... probably needs changing. 

Thanks for any help.


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## MiamiAG (Jan 13, 2004)

Hi,

I have a similar situation. I usually bring the pH down from around 8 to 6.8 in the matter of 30 minutes after a water change. To date, I've had no problems with the fish.


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## Tiptoptank (Mar 28, 2005)

I do straight tap water changes of 50% on my discus tank twice a week and the Ph does swing a bit but, I have not had any problems. 

If you want to do it right you would need to age the water. Setup a food quality drum (20-100gall) and place a large airstone in it and a good pump. Pour your tap into it and let it stand for 24 hours then pump it in the tank. You can also add your buffer in the tank leaving the you W/C's without PH swings. 

I have been thinking about doing htis myself in th e near future.


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## abwalker (Feb 25, 2005)

I suppose I would have to run CO2 through the air stone? The problem is that the tap has a high pH and the tank has a low pH due to CO2 injection. Simple aging does the opposite and brings low pH tap to a higher pH by driving off dissolved gasses. I suppose I could add bicarb to the tank slowly to make up for the replaced water. That way I would be adding unbuffered 7.2 to the tank, rather than buffered 8.2-8.4. Of course, that defeats the purpose of not spending the weekend with the fishtank. I would then slowly add buffer as the CO2 re-reached the desired concentration and the pH dropped below where I want it. If I could figure out how long that takes, I suppose I could put it in a Kent doser or the like. 

I guess why I am concerned/surprised/confused, is that like Art said, people regularly do large water changes while injecting CO2 and don't have a problem. Maybe I should just not worry (yeah right...). And the pH monitor was supposed to make things simpler... my prior ignorence was bliss!! 

I guess I could T-off the CO2 line and pretreat my waterchange water prior to starting... I wonder how long that would take or how much gas I'd be wasting... 

Thanks for any input. 
Abby


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## ardvark (Feb 26, 2005)

Hi Abby
In my opinion save yourself some headaches and just do your water change and forget about pH swings. If you start making a science project out of water changes you're not likely to keep it up for very long as a result of the incredible tedium you just described (wow, my head is still spinning).

In tropical rain forest streams, pH swings occur all the time such as when it rains or when tannic acids leach into the water from debris, or when the stream floods, or even when the fish swim into a different stream. The fish will get over it. In fact, many of the natural pH and temperature swings signal the onset of the breeding season. What they won't get over is pollution due to poor maintenance, so keep it simple so that you will encourage yourself to be consistent.

Art summed it up in a nutshell in his one liner response. He has a 10 fold swing in pH every water change, and that occurs twice - when you add the new water you get an increase and then as the CO2 injection pulls the pH down you get a decrease. No problems.

Cheers,


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## Sir_BlackhOle (Jan 25, 2004)

Maybe you could turn your co2 off one night, and the next morning do your water change and turn the co2 back on?


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## shalu (Oct 1, 2004)

I do water change straight from tap 50% x2 weekly in my discus tank. Even stop CO2 at night now. Fish never complain about ph swing.


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## plantbrain (Jan 23, 2004)

The issue is not pH, it is CO2 content.
pH is just a measurement, if you add -HCO3, KH, then this will effect the fish if you add a lot rapidly.

We use pH to measure CO2 content, we add CO2 to fertilize the plants, not for "pH control".

The KH remains the same, the salt content remains the same, everything pretty much except the CO2 content.

Fish exhale CO2 and take in O2.

You can measure the O2 before and after a water change.
Note fish and shrimp behavior before and after.

You'll see a correlation between hyperactive critters and high O2 levels.
CO2 has little impact unless very high as long as there is good O2 levels associated with it.

So focus on the base of food chain/ecosystem if you want to provide a happy home for the higher trophic levels like shrimp and fish and I suppose us.

Regards, 
Tom Barr


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