Changing KH - The Planted Tank Forum
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post #1 of 3 (permalink) Old 02-22-2006, 08:50 PM Thread Starter
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Changing KH

When I started my 40 gallon tank in Sept my KH was at 5. Six months later, it tests out at 4 on Sunday, my water change date (50%), and drops to 3 by Wednesday. Iím shooting for consistent injected CO2 and, though my bubble count is consistent, this causes my ppm to change through the week.

Is this normal and should I be boosting my KH?

One of my concerns is that Iíve now had 2 bouts with BBA and I read somewhere that inconsistent amounts of CO2 can be a cause. My tank is fairly thick with plants and my growth rate is great.

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post #2 of 3 (permalink) Old 02-22-2006, 10:18 PM
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What's your tap KH?

Is your substrate EcoComplete by chance? I have very soft tap water, but Eco raised KH in my 29G from undetectable to 6. In my case, water changes would gradually bring KH down (like what you're seeing) were it not for the hardscape dissolving due to acid from CO2 injection.

Obviously baking soda is your friend, but I wouldn't start messing with water chemistry until you figure out the steady state, especially if your CO2 is automated. If your KH is being driven up or down, pH will follow and automated systems will attempt to compensate. This can kill fish at extremes.

Example (from my very own tank):
Hardscape dissolves, raising KH
pH rises with KH
(If my CO2 was automated) System injects more CO2 to lower pH
Increased acid causes KH to rise
pH follows, and system again tries to compensate by injecting more CO2
You see where this is going...
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post #3 of 3 (permalink) Old 02-23-2006, 01:13 AM
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A changing KH doesn't change the amount of CO2 in the water. If you get what you want at 3 bubbles per second, you will have what you want even if the KH changes. The exception is when you start with too low a KH and the CO2 drives the PH much too low for the fishes to tolerate. But, KH shouldn't change very much through the week unless something is buffering the PH.

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