How long until pH change??

[fishfrenze]

Hello,
I set up DIY CO2 (yeast method) on my 72 gallon tank on Sunday. At first I used 1/4 tsp. yeast + 2 cups of sugar for the mixture and had 2 bottles. I was getting one bubble/second, but it didn't seem to be making a difference in my pH. Yesterday afternoon I changed the mixture to 1/2 tsp. + 2 cups of sugar in both bottles. It's tough to estimate the bubbles b/c 15-20 will come out in 2-3 seconds then none for 5-10 seconds so its hard to count accurately. I'm probably getting about 1.5 bubbles/sec though and its been about 12-18 hours since setting up the new mix so it may increase. However, my pH has only decreased by about .1-.2. There is a ton of CO2 in my reactor b/c it is not dissolving fast enough...I'm using the gravel vac/powerhead method and there is about 2 inches of CO2 at the top of the vac. I know the CO2 is getting in there, but why is my pH staying so high? How long does it take before you start seeing changes? Should I add a third bottle?

Melanie

P.S. my pH is orginally 7.6 with a KH of 3 dH. My target pH is about 6.8-6.9.

[superjohnny]

It usually takes a day or so for it to start making bubbles. You need to give it a little more time to work. 1 2ltr bottle of DIY CO2 should last about two weeks.

<edit> with a kh of only 3 you don't want too much CO2 or your PH will crash. If your PH is around 7.4-7.6 it's fine.

[RTR]

??? If the KH is 3, and the pH is 7.6, and you have not added buffers of any sort, per the tables you have a CO2 level of 2.2ppm. If it has dropped only 0.2, that would only be 3.5ppm. That is low for even atmospheric equilibration unless you live high in the Rockies. It is not fine if you are trying to add CO2.

Have you checked the CO2 generator and all associated tubing for leaks?

How much surface agitation do you have? HOB(s)? Biowheel(s)?

[Tempest]

If you have the gravel tube filled up with CO2 like that, there isn't much chance for it to dissolve like it should. Sometimes a batch will start off doing that on me.. I take off the gravel tube and let it escape then put it back on so there is more room for water in it if that makes sense. The DIY will level out more after that initial burst so the powerhead can keep up. It is real hard to keep enough CO2 in my 55 gallon even with two bottles so I can imagine you are going to have a lot of problem keeping it up on a 72 gallon. I wouldn't set up such a large tank without compressed. My 55 gallon is gonna get that as soon as I can budget it in. :D

[djlen]

I have a kH of 3.5 and was using 4 - 2 liter bottles to get 20 ppm before I switched over to pressurized.
I think you'll find that your tank is just too big to make DIY a feasible option.
I can't understand why while using a power head, you are getting CO2 stuck in the siphon tube. Use that same type reactor an rarely get any left in there at all.
All you need to do to check your bubble rate is to shut off the power head and count the bubbles going in. Then restart and you're in business.
Len

[fishfrenze]

How much surface agitation do you have?
I had bubble bar going (just because I like the look) and didn't think it really made that much surface agitation, but I shut it off yesterday morning to see what happened. Since then, the pH has dropped another 0.2 or so. I guess it was too much! :)

If you have the gravel tube filled up with CO2 like that, there isn't much chance for it to dissolve like it should. Sometimes a batch will start off doing that on me..
By the afternoon the powerhead caught up and now it has all dissolved.

I think you'll find that your tank is just too big to make DIY a feasible option.
I agree...however, my apartment building does not allow pressurized gas tanks of any kind so I'm stuck. Plus, I can't afford to set up the pressurized system right now. :) I'm willing to do the excess amount of work to keep it up and going until I move. I figure if I alternate the bottle changing...change one every week, I should be able to keep the CO2 levels pretty consistent.
I will add another bottle this afternoon to see if I can reach a pH of 6.9. Since I haven't put fish in yet, if the pH crashes, this is a good time to do it!

Thanks for the help!
Melanie