Ph, kh and co2... - The Planted Tank Forum
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post #1 of 6 (permalink) Old 07-29-2005, 06:48 PM Thread Starter
Algae Grower
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Ph, kh and co2...

I have a rather odd question caused by something I can't explain and have no idea as to the cause.

My tank is a 75g with tahitian sand substrate. It is moderately planted and have had Co2 running for about 6 weeks.

My tank's water is 7.5 ph when it has been outgassed with a kh of 10. My tap water after it has aged for 3 days has a ph of 8 and a kh of 10 degrees.

Why is my tank's ph lower then my tap? I have not been able to figure this out. Also considering the above, what should I be lowering my ph to with the co2 to have a healthy enviroment for my fish?

Thank you!

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post #2 of 6 (permalink) Old 07-29-2005, 06:55 PM
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the reason why your ph is lower in your tank is cause u are adding co2 i would up your co2 to 30+ ppm drop your ph to 6.8 to 7

29 gal tank 2 55 watt coralife with GE 9325K diy co2 100% Eco-Complete
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post #3 of 6 (permalink) Old 07-29-2005, 07:30 PM
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If you don't know about the CO2 chart, used to calculate CO2 level based on pH and KH, then you really should learn about it, as it's how you monitor the levels.
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post #4 of 6 (permalink) Old 07-29-2005, 07:49 PM Thread Starter
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I know about the Co2 chart. I have checked that out previously.

I guess my concern is surrounding the fact that my tank has a Ungassed- No Co2 in it - ph of 7.5 and 10 degrees KH. These parameters tell me that I have co2 present in the tank, at about 10ppm with NO CO2.

Should I disregard this?
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post #5 of 6 (permalink) Old 07-29-2005, 08:53 PM
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fish give off "some" co2, but shouldn't be influencing it that much.

the 10KH giving 8pH is based on the atmospheric level of co2 being 3ppm, so it is right on target for your tap water results.

Also, what is your fish load like? As you feed fish and they produce waste, the acids will eat away at your KH a little bit. This is one of the main reasons for having a KH of above 4 in a non-planted tank. By saying that your pH is 7.5, that would imply a KH of 4 though, which is very doubtful that other factors are pushing the KH down. And you said it is still 10 KH anyway upon testing.

How sure are you that your KH levels are not dropping?

110g - Vivarium (Dart Frogs)
180g - Reef
100g - Planted Tank (mainly Swords)
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post #6 of 6 (permalink) Old 07-29-2005, 09:19 PM Thread Starter
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I just tested the tank's Kh...came back as 10. This has been constant for the last 4 months or so...the Kh has never dropped.

Fish load is rather light right now... 2 gold fish ( don't ask...they are just there ) 6 cories, 3 dojo loaches, 6 tetras, 3 bettas, 2 dwarf gouramis...
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