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Old 09-08-2003, 12:13 AM   #1
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Questions regarding pH/KH

I broke down and did some study and now have a much better understanding of pH and KH as it relates to dissolved CO2. Assuming there is a direct relationship as shown on the charts, the use of CO2 is merely a method to reduce pH while keeping KH constant (indirectly increasing dissolved CO2), not to directly add CO2 to the aquarium to be utilized by the plants. It appears that if one uses a "conditioner" to lower pH, you're lowering KH at the same time which is counter productive (basically, the higher the KH and the lower the pH the greater the dissolved CO2). If KH and pH are both reduced, unless KH can be maintained @ that level, both KH and pH will likely increase w/water changes and such. Also, if KH gets too low large pH swings are likely which are even more problematic for fish and plants.

All that being said, is there some commercial pH reducer that reduces pH, while leaving KH alone? (other than CO2) I measured my KH and pH today with a KH reading of about 6.0 and a pH of about 8.0. Though the measurements were taken late in the day (after the tank lights had been on for approx. 9 hrs.) I doub think the pH is going down enough @ night to get an adequate supply of dissolved CO2 built up. I would like to keep my KH where it is but reduce the pH. Is there another way other than CO2?

Does anybody know anything about the Carbo-Plus?-- uses a carbon block to create carbon dioxide.

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Old 09-08-2003, 07:39 AM   #2
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The ph value of your aquarium water descibes wheather the water reacts acid, neutral or alkaline. The carbonate hardness makes sure that the measured ph value remains stable.
The lower the carbonate hardness, the more unstable the ph value will be, but the easier to change. In a communty tank you want a ph of 6.5-7.5 and a carbonate hardness of 4dKH-10dKH.
If you have a ph of 8 then you carbonate hardness will be 4dHK-6dKH, by using a peat in your filtration system or useing R/O you should be able to bring your ph down and still keep it in the scale required.
I am not an expert on this subject and there is probably someone who could help you more, but i hope this helped.
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Old 09-08-2003, 05:54 PM   #3
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Sorry, I couldn't resist. Peat is an excellent way of lowering one's PH. Kent Marine also makes a fine product called PH Minus. Of course, plants will lower your PH too.
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Old 09-08-2003, 09:17 PM   #4
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The Carbo-Plus is a poor substitute for a pressurized system. And in fact the Carbo-Plus costs more to run over the long term than does a pressurized system. And I hate to tell you this but the CP unit works by reducing the kH of the water to CO2. So if you have water with low kH you will have problems with the Carbo-Plus.

And if you are not injecting CO2 your levels will not go up. Your pH might vary .2 points day to night but even then that just gets you to what normal stable values are in non-injected water. Injecting CO2 does lower the pH but it also gets more CO2 into the water column for the plants to use. You are about half way to understanding that.

With a kH of 6 you will be hard pressed to use any additive other than CO2 that will lower your pH and keep it down. With a kH of 6 your water has a pretty good buffering capacity. Any chemical additives you use (other than peat which is another story) will just cause your pH to bounce around like a ping pong ball in a hurricane.

I have to ask what your tap water or the water source you are using for the tank has for pH and kH.
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Old 09-08-2003, 10:09 PM   #5
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I guess I'm looking for a short-term solution. Eventually, I will likely have to go with pressurized CO2. I guess the main reason I don't want to is because I had a nice dual stage Lifereef Ca reactor that I sold with my reef stuff. I could have thrown some bioballs in one of the reactors and voilla, a wonderful plant system.

I'll check out the Kent stuff, but my guess is that it will also decrease KH. I did some reading on the Carbo-Plus and discovered that it also tended to reduce KH.

Rex, if you subscribe to all the tables showing the resulting dissolved CO2 @ various KH/pH values, adding CO2 would have no direct effect on CO2 levels. Indirectly, the pH decreases while KH remains constant, hence dissolved CO2 increases tremendously. With the addition of most pH stabilizers, pH and KH both decrease, hence CO2 only marginally increases. This is one of the many tables available on the Web:

The relationship of CO2 , pH and KH
\ pH | 6.0 6.2 6.4 6.6 6.8 7.0 7.2 7.4 8.0
KH\ | -----------------------------------------------------------------
0.5 | 15 9.3 5.9 3.7 2.4 1.5 0.9 0.6 0.2
1.0 | 30 19 12 7 5 3 1.9 1.2 0.3
1.5 | 44 28 18 11 7 4 2.8 1.8 0.4
2.0 | 59 37 24 15 9 6 4 2.4 0.6
2.5 | 73 46 30 19 12 7 5 3 0.7
3.0 | 87 56 35 22 14 9 6 4 0.9
3.5 | 103 65 41 26 16 10 7 4 1.0
4.0 | 118 75 47 30 19 12 6 5 1.2
5.0 | 147 93 59 37 23 15 9 6 1.5
6.0 | 177 112 71 45 28 18 11 7 1.8
8.0 | 240 149 94 59 37 24 15 9 2.4
10 | 300 186 118 74 47 30 19 12 3
15 | 440 280 176 111 70 44 28 18 4

| CO2 milligrams/liter -------------------------
---------------------------------------------- -------------------------

Sorry this table is a little wavy. However, it can be found @ many places on the internet. Here is a link:


I haven't measured my tap water in some time. When I kept reef tanks, I only used RO/DI. I can tell you that probably around 1/3 of my water is RO. I have an automated top-off system that supplies RO. My weekly water changes are tap.

I am somewhat interested in using peat. However, I've heard that it doesn't work well in hard water. If I decided to use, what amounts would be necessary and what is the best way to introduce?
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