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mr hyde 08-01-2003 05:16 AM

I've been mixing 1 part tap water to 5 parts RO water to get a PH of 6.8 before adding it to the aquarium. Once it's in the tank it never seems to go up or down much at all which is good. What I'm wondering is what PH do most of you have to start out with before injecting CO2 and bringing it down. I've heard of a lot of people having a PH of around 7.2-7.4 and then adding CO2 to bring it down to 6.8 and using a contoller to keep it around there. Mine is always at 6.8. If my CO2 stops it still stays at 6.8 and after a day of plants using it up it still seems to stay the same. I'd like to add more tap water because my GH and KH is really low but am wondering if I'll still be able to get my Ph down to a decent level if I start out at a PH of 7.2. Adding the extra tap water will raise the PH. It seems like from what I've heard others say that if I'm starting with a PH of 6.8 from the start then once it's in the tank with CO2 being added it would be going down lower like to 6.0 which wouldn't be good of course. Maybe I should just leave it alone. The reason I ask is I'm thinking of adding a PH controller and if my PH is always at 6.8 then the monitor would be reading everything as ok and not ever adding CO2 even though there would be a need for it. I hope I explained this right. Thanks

Rex Grigg 08-01-2003 12:42 PM

What is the size of your tank and are you using DIY CO2 or pressurized? Also what are the kH and gH readings in your tank?

mr hyde 08-01-2003 05:18 PM

This is a 46 gal tank w/DIY CO2, 2 bottle set up, going into the filter intake of Eheim. The KH is 70mg/L and the GH is below 20mg/L. This is using a Hagen test kit, hopefully it's accurate. I haven't tested the CO2 in the water yet.

Angel12 08-01-2003 05:53 PM

If I have converted right then Your KH is 3 and GH is 1 ..
Take a look at this table it is very informative and will enable you to work out the correct PH you need to hit for maximum benefit

from your current readings 6.8 is right for the amount of Kh you have could take it down to 6.6 ...


Guttboy 08-01-2003 06:34 PM

My tapwater is 7.8 pH, KH 125, GH 143

Will drop pH here when I get the CO2 system on monday. Will let you know how things work out!

Mike :D

Momotaro 08-01-2003 10:20 PM

I do just about the same thing, mixing RO and tap water. Out of the tap my pH is about 8.2, a wee bit high for my taste. My tap / RO mix brings my pH to 7.2 and my KH to 4. I then inject CO2 and bring the pH down to 6.8.
Since you are using DIY CO2 injection, not pressurized, how do you plan on using a pH controller? You need a regulator and solenoid to run a controller.


Bumping your KH up a wee bit might not be a bad idea.

mr hyde 08-02-2003 04:29 AM

I'm planning on getting a controller soon with pressurized system. I was curious as to what PH to start out at before injecting CO2. I'll probably be adding more tap water to the tap/RO mix to bring the PH up to around where your's is instead of 6.8 where I am now. Then bringing it back down with CO2. Thanks , much appreciated!

m.lemay 08-02-2003 11:20 AM

Keep your kh around 4-5 degrees. That'll give you sufficient buffering for co2 injection. Ph readings can be very deceptive with water that has a low buffering capacity. Use kh values instead of ph to set buffering.


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