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very confused about relation between pH/KH and CO2 lvls
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ATC
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Joined: 16 Feb 2011

PostPosted: 2011.02.16(Wed)20:54    Post subject: very confused about relation between pH/KH and CO2 lvls Reply with quote

I have tested my water for pH and it is showing as 6.0 pH, my KH with 5ml test is showing as 0-1KH as 1 drop instantly turned yellow, did with approx 10ml and 2 drops were required to turn yellow so 0.5-1.0 KH (will be taking my water in to the LFS to have them confirm my readings).

With these numbers it seems that if I am understanding things correctly is that I have minimal buffering capacity and therefore can have fluctuations with pH and that the chart is telling me to increase my KH.

I want to do a planted aquarium with the addition of CO2 via DIY but am not clear as to the route I should take to "stabilize" my pH. Should I add alkaline buffers, ie: Seachem alkaline buffer ( will increase both), or should I do a pH up and if so, to what range and what product would you recommend?

I want to understand this completely before I go ahead and fail miserably, lol.

Input is very much appreciated.
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UncleWillie
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Joined: 26 Nov 2007
Location: Georgia, USA

PostPosted: 2011.02.16(Wed)21:59    Post subject: Reply with quote

I know very little about this subject, but had issues in the past with extremely low alkalinity/KH. What I know is low KH means that your tank may be prone to crashes in pH and CO2 tends to be become more of a problem with low pH. For those who use rainwater in tanks, know that rain tends to be acidic (low pH) and will already have high levels of CO2 in it already.

For my issue about 3 years ago, I was directed by the LFS to buy a certain product to aid in this (I can't recall the name), but I found it to be an expensive and temporary fix to the problem (especially with multiple tanks). At the time, being pushed for money, I ended up buying a bag agriculture lime and giving the rest to friend starting a garden. I put a relatively thin layer underneath my substrate to increase buffering capacity. Many here may be able to back this up - but crushed oyster shells have the same effect. I think oyster shells are more commonly used in aquaria though. I actually think bags of lime and oyster shells were next to each other at Home Depot.

Anyway, hopefully someone can give you some info on great products designed for aquaria, and help you out further. This way you won't have to be a cheap-o like me, and you won't have to buy in bulk Smile
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unissuh
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Joined: 29 Mar 2005
Location: Melbourne, Australia

PostPosted: 2011.02.16(Wed)22:05    Post subject: Reply with quote

Typical recommendation is to add sodium bicarbonate (supermarket stuff is perfectly fine) until you get a KH of 2-4. With the ~30 ppm of CO2 that is considered ideal, you should end up with a pH of approximately 6.4-6.6. It's about 3 grams per 100 L to raise KH by 1; a teaspoon is about 5 grams.

The other option is to add a few crushed shells or coral in a little bag in your filter to keep up (both GH and) KH.

EDIT: Realized this might be a bit brief when looking at it again, just let us know if you need any clarification or have any other questions. Very Happy
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Last edited by unissuh on 2011.02.17(Thu)2:00; edited 1 time in total
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UncleWillie
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Joined: 26 Nov 2007
Location: Georgia, USA

PostPosted: 2011.02.16(Wed)22:22    Post subject: Reply with quote

Ah-ha! I knew someone who knew what they were talking about would have a good explanation and recommendation. Very informative. I know what to do next time I have this issue!
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ATC
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Joined: 16 Feb 2011

PostPosted: 2011.02.17(Thu)7:08    Post subject: Reply with quote

Seems like baking soda is the way to go to get things where they need to be. Now for clarification, once I get my KH to around 3-4 and inturn my pH levels will rise, will those figures stay constant until my water changes? if so great, as it will be a minimal amount of work to stabilize my water.

Based on the CO2 chart it seems that having a pH of 7.0 is best as it allows for the widest range of KH with ideal lvls of CO2, if this is truly the case, should I just continue to add more baking soda to get to those lvls ?
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unissuh
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Joined: 29 Mar 2005
Location: Melbourne, Australia

PostPosted: 2011.02.17(Thu)7:18    Post subject: Reply with quote

You just need to add the right amount of bicarb into fresh water when doing water changes. KH shouldn't change all that much by itself in the tank (months at least typically).

I think you are reading the chart wrong. The chart gives you the pH that comes about from different levels of CO2 vs KH present in your tank. If you alter pH by another means besides via KH, you are just making the chart invalid for your situation. It assumes there is zero interference from other chemicals (not always the case).

30 ppm of CO2 is considered ideal as this is about as high as one can safely go without suffocating fish. Raising CO2 much more apparently also doesn't result in much faster plant growth, which is why people don't tend to raise it much higher. The reason why people tend to aim for 2-4 KH with 30 ppm CO2 is because they end up with a pH in the mid 6s which is ideal for most fish that suit planted aquariums.
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ATC
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Joined: 16 Feb 2011

PostPosted: 2011.02.17(Thu)7:28    Post subject: Reply with quote

that makes sense to me. I appreciate you explaining to me how to read and understand that chart. It was giving me nightmares, lol. Apparently I did not do so well in chemistry class.

I will work on getting the KH in the 2-4 range and then maintain that.

Thank you for the input and awsome advice, I will keep everyone posted as to how the transformation is coming along with my tank once I start the planting process.

thanks again
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DaleJr
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Joined: 16 Feb 2010
Location: Memphis, TN

PostPosted: 2011.02.21(Mon)15:16    Post subject: Reply with quote

Also something else you might want to do is call your local water department and ask them for the last water anayist so you know EXACTLY what is in your water (minerals) for your plants so you will know how to adjust accordingly.
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ATC
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Joined: 16 Feb 2011

PostPosted: 2011.02.24(Thu)13:07    Post subject: Reply with quote

I did get a report from my water supplier and found out that my pH from the tap is at 7.2-7.4 a far cry from the 6.0 reading I was getting earlier.
The KH has also been confirmed to be very low 17 mg/l, so I have added some baking soda to the water (slowly) and got it up to around 3-4 dKH and when I tested the water parameters the following day, low and behold, pH 7.2-7.4 (the colors are so similar that I cannot tell, damn you eye balls) and the KH at 3
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