Question about CO2 and Ph with water changes

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yohann976

Aquarium Advice Freak
Joined
Mar 14, 2006
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Right now, I am using Excel as a CO2 substitute, but it is becoming more of a pain than it is worth. Especially because I have a 90 gallon tank, and I go through a large amount of Excel very quickly. So I think I might go with a pressurized CO2 system.

My tap water is at about 7.5 Ph and it is very hard. The test strip indicates that the GH is around 100ppm and the KH is around 200ppm. Lets say that I want a CO2 level of 30ppm with a target Ph level of 7.0 (this is according to Chuck's calculator). What happens when I change 50% of the water? Wouldn't the PWC immediately change the Ph from 7.0 to 7.25 until the CO2 could be dispersed? I have discus and I don't think that they would like that. BTW, they seem to be fine with the higher Ph, but probably not a Ph swing.
 
Yes it would chnage but the Co2 would drop it back quickly. The PH swing from the CO2 is not going to bother anything, as long as the KH is constant. If your tap KH and tank KH is close you have nothing to worry about. It is KH changes that bother FW fish not PH swings.
 
During the PWC a lot of the CO2 would be off gased as you mentioned. but the change in pH would not be that stressful to the fish. the change in KH is what is stressful to fish.

HTH

EDIT: I see Rich beat me to it. LOL
 
I was also worried about this pH swing, but as rich and rkilling have stated, it will not bother your fish.

If you decide to use a pH probe / monitor with your pressurized setup, make sure to turn it off during PWC. When the probe comes out of the water it goes crazy, resulting in a huge amount of CO2 injection. My tap is around 7.9 pH and 120ppm kH and I inject down to 6.9. After PWC it is between 7.1 - 7.2 and corrects itself in an hour or two. The fish have never showed any signs of stress (though I don't do discus).
 
That is a relief. What is a good CO2 system to use? Also, is a Ph monitor that hooks up to the system worth the extra money?

Oh yeah, one more thing; is it possible to hook the system up to two tanks. I have a 46 gallon bow front tank just sitting here begging to become a planted tank. lol
 
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