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Discussion Starter · #1 ·
I have a 20 long tank with a significant amount of plants and 16 fish. I am using the hagan C02 system with 1/4 tsp of yeast and 1/4 tsp of baking soda every 2 weeks.
I have soft water. I have only recently been monitoring my PH, which is between 6.2 and 6.6. I have also been testing my KH.
I'm wondering if I need to test KH very often. Will KH change within the tank? I change water 25% every Wednesday and Sunday. Should I expect my KH to remain where it is around 2, or does it fluctuate?
 

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KH will remain pretty constant, and your water changes will tend to keep it very constant. I'm assuming you are not adding any baking soda or other KH changing substances with the water changes.
 

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Discussion Starter · #4 ·
I am not adding anything to the water. I'd prefer not to. But I am starting to monitor PH now to see if I do need to do something to increase buffering capacity. My plants seem fine, and my fish seem fine. I'm just want to be more certain that my fish are fine.
I'll continue monitoring PH to see if it stays as consistent as it appears to be with my limited testing.
 

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Contrary to popular belief, increasing the KH has no effect on how much fluctuation in pH you will have. Increasing KH just increases pH, but it doesn't stabilize it at all, unless your starting KH is very, very low, perhaps less than 1 dKH.
 

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Monitor both, and see how your tank runs.
Decomposing organic matter can use some carbonates, and nitrifying bacteria can use some.

If the KH does drop, and you want to keep it a bit higher you can add potassium bicarbonate or sodium bicarbonate (baking soda).

The pH will probably follow a daily cycle. Higher when the plants are most actively removing the CO2, and lower pH through the night as the CO2 accumulates.

Raising the KH a small amount will not alter this daily cycle of the pH, and fish are just fine with this daily cycle, too.
 

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Discussion Starter · #7 ·
Contrary to popular belief, increasing the KH has no effect on how much fluctuation in pH you will have. Increasing KH just increases pH, but it doesn't stabilize it at all, unless your starting KH is very, very low, perhaps less than 1 dKH.
I used the 10ml in a white cup method to try to get a better KH reading. It turns out my KH is 1 dKH. This was the result at the end of 12 hrs of light and the result 1st thing this morning after 12 hrs of dark. I use an air stone to add oxygen at night since I have the continuous C02 drip.
So,
a. sounds like my KH is right on the edge. Should I tinker with it?
b. what does stabilize pH?
 

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I used the 10ml in a white cup method to try to get a better KH reading. It turns out my KH is 1 dKH.
That is certainly low, but it just means your pH will be lower than it would be if the KH was higher. Most plants do well with low KH.
This was the result at the end of 12 hrs of light and the result 1st thing this morning after 12 hrs of dark. I use an air stone to add oxygen at night since I have the continuous C02 drip.
So,
a. sounds like my KH is right on the edge. Should I tinker with it?
I wouldn't tinker with it, but you can if you wish. Just use ordinary baking soda to raise it. The problem that causes is that you then should adjust the KH of the change water every time you do a water change. I don't see any real justification for doing that.
b. what does stabilize pH?
The pH of the water is a variable depending on how much CO2 is in the water, what the KH is, how much tannic or other organic acids are in the water, etc. It isn't necessary to stabilize pH. Whatever happens to the pH, it happens slowly, so the fish aren't harmed.
 
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