# Ph 6.5 and Co2 off



## e.lark (May 5, 2005)

Alittle confusion regarding the Co2 chart. Adding Co2 lowers the Ph therefore you are able to get a reading based on Ph and Kh readings.

Well, now my Ph is stablizing at 6.5 by just doing water changes. My Ph monitor attached to the Co2 regulator is no longer kicking on because the Ph is not rising high enough. Plant growth seems ok while I'm still dosing ferts but I never see the Co2 kick on anymore. I am starting to see alittle bit of algae on some driftwood.

My water changes have always consisted of 3/4 RO water to 1/4 tap, 50% weekly. Do I need to start adding more tap water than RO when doing water changes or should I add some baking soda to the tank? Our tap water has a very high TDS reading with a Ph of 8 or more.

set me straight on what I should be doing.


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## Simpte 27 (Jul 16, 2004)

If your Tap is 8.0 then I would venture to say your co2 is running. R.O. water has a ph of 7 so something is dropping your ph. What is the kh of your aquarium?


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## alexperez (Oct 8, 2004)

Make sure that the Controller is calibrated?
have you added the driftwood recently?


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## fish7days (Jul 30, 2005)

Make sure your probe is clean. I cleaned mine the other day and it was 2 points off, meaning 2/10 of a full scale increment. I then re calibrated and now it looks good. Don't be shy to turn it down to 6.1 or 6.2 if your fish/plants can tolerate it. I keep mine right between the two and plants and fish do fine.


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## e.lark (May 5, 2005)

Thanks, I attempted to calibrate the probe about two weeks ago and it didn't need it. I have both the 4 and 7 solutions.

At the same time I did test for Kh a couple weeks ago as well. I can't tell you what it is reading today since I'm at work but acouple weeks ago it tested around 3.5 to 4. That is why I'm confused. With those readings I should be right around 30ppm Co2 but I never see the regulator kick on anymore.

I did change out my driftwood a couple months ago....I put in a new peice of what I think is Manzanita driftwood.. do you suppose this is releasing tannins and lowering the Ph to 6.5?


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## e.lark (May 5, 2005)

I was mistaken in that my Kh is actually lower than I had thought. I am now getting a reading of 2.5 rather than the 4 that tested before this problem started happening. The relationship of of Ph to Kh is not something I fully understand so I am still unsure how this affected my low Ph reading or if it really does at all.

I'm looking for a fix and searching the site I think adding baking soda would be the best bet to raise Kh back up to to where I had it. I understand this will also raise Ph and now I'm completely confused on how I am to determine Co2 levels since most of these posts were not written for the layman. Could someone explain if my error in the kh reading has anything to do with my ph not going back up to 7?


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## dennis (Mar 1, 2004)

whooooo. Lets see if I can explain this simply.....

Basically the lower you kH, the less work it is for acids (like CO2) to lower the pH. Generally speaking, kH stands for carbonate hardness, which is a measure of the CO3 ions in the water(I belive it is actually CO3+) NOw when you dissolve CO2 in the water you get CO2 + H20 -> H2CO3, or carbonic acid, which as acids do will lower the pH of your water. 

The amount of CO2 that can physically be dissolved in water at a specific pH is totally dependant on the kH of said water. All of this means that a lower kH, less buffer, is more easily affected by the CO2 you add. Meaning that the pH will drop much quicker and easier with the addition of CO2 (converesly the pH will raise faster when CO2 addition stops)

In the end this affects you because at kH 2.5/ pH 6.5 you have approximately 15-20ppm CO2 (I don't have a chart in front of me and I am going by memory here but the CO2 would not be higher than that) However at a kH of 4 and pH of 6.5 you have like 30-35 ppm CO2. SO yes, you errant kH reading is the cause for your issues, you have less CO2 in the water than you thought you did.

It is all actually much more complicated than that but that is the basic jist of things. Hope that helps


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## e.lark (May 5, 2005)

Yes thank you, it truly does but...The original issue is that Co2 has not been kicked on by my ph controller for some time now because the Ph is settling at 6.5 and will not go any higher thus the no Co2 is being injected into the tank.



dennis said:


> SO yes, you errant kH reading is the cause for your issues, you have less CO2 in the water than you thought you did.


what I'm saying is as far as I know there is no Co2 in the water at all.

I'm fine with keeping my Ph lower than 6.5 but I would like to figure out why even without the addition of Co2 my Ph does not go back up. I'm afraid that if I lower the ph controller to kick on at 6.3 then the Ph will start to settle below this, then 6, etc... Whats making it so low?


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## dennis (Mar 1, 2004)

Start by lowering the pH setting on your controller to 6.3. Set out a glass of water tonight and in 24 hours recrehck the calibration of your probe, check the pH of you rtank and the test sampleusing your probe and double check the kH of the test. Next go look at a CO2 chart,  here is one to start you off and compare your readings. I am guessing that a degassed, settled out sample of your tank water will test between 7.4 and 8.0 pH This is what your water with a kH of 2.5 should have due to CO2 levels in the water at ambient air levels.

You should have adequate Co2 levels in your tank with the controller set to 6.3-6.4pH It would be logical that your tank pH would settle out around pH 6.5 if you don't have much surface movement or CO2 degassing from surface movement. Your CO2 probably runs for a short time in the morning when the controller turns it on then the level never really falls for the rest of the day. 
In my tank, with a kH 4 and little surface movement good CO2 levels are around pH 6.5 yet in the early morning the pH would only be 6.7-6.8. Increasign teh surface movement casued the tank water to be 7.0 in the morning, same as a settled, degassed sample. Your findings and experience does not suprise me

I woudl lower the controller to 6.3 and keep an eye on it. If you get some fish stress go up to 6.4. You should not have any issues with the pH droppin glower than the controller is set unless your kH drops below 1. Do remember though that the Milwaulkie controller has a .2 varience in its setting. If you have it set for 6.3, it will comevon at 6.4 and turn off at 6.2. This is normal and nothing to be concerned about.


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## e.lark (May 5, 2005)

cool, thanks Dennis


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