confused about CO2, ph, kh, etc. - The Planted Tank Forum
 
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post #1 of 12 (permalink) Old 02-12-2008, 10:49 PM Thread Starter
 
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confused about CO2, ph, kh, etc.

Okay, I'm totally lost in this whole water chemistry thing.

Prior to adding pressurized CO2 to my 90g, my pH was around 7.2, KH was 10ppm. Based on those figures, my water should've had around 1ppm CO2 just naturally dissolved in the water.

Hardly enough for good plant growth under my lighting.

So, I added a pressurized CO2 system which came with everything - needle valve, bubble counter, reactor, even a little drop checker thingy that sits in the tank. Plant growth is doing great, and I'm getting some pearling. I've been dosing with an NPK pre-mix by Hagen, which hasn't given me thrilling results. The ferts I ordered from Rex Grigg arrived today.

Since adding the CO2, my pH has gone down from 7.2 to 7.0, and my KH has climbed from 10ppm to 40ppm. According to the little chart, this means I'm now at a whopping 6ppm CO2. whaaaaat?

I'm so confused. Does pH and KH seriously limit how much CO2 I can get into my water, even with a pressurized system? The little drop checker goes a nice shade of green when I keep it running at about 3bps, but I'm just using tank water in it (which is what the manual says), so really, isn't it just telling me the pH of that water sample?

I'm not all that eager to manipulate my KH, GH, or pH, as they're all in desireable ranges. My pH is, as mentioned, 7.0, KH is 40ppm, GH is 80ppm. Perfect for my tank, since all the fish I have prefer soft, slightly acidic water. I'm surprised my pH has stayed at 7.0 (it comes out of the tap that way), because I've got driftwood in the tank, peat in the filter, am running CO2, and don't have anything in the tank to raise the pH.

How can I get my CO2 up to the desired 30ppm?
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post #2 of 12 (permalink) Old 02-12-2008, 11:11 PM
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First, I would ignore the charts. I keep reading that they are woefully inaccurate. I don't know why your KH went up and your pH went down only slightly with the addition of CO2. But I wouldn't worry about either of those and rely on your drop checker, which needs a little tweaking. In order to accurately know the amount of CO2 in your aquarium, you need to use a standard solution in it. Most people use a 4 dKH (or 4 degrees of potassium hardness) solution in their drop-checker. Then, when it turns green, you know you have 30 ppm (parts per million) of CO2 in your aquarium. If you use aquarium water in your drop checker, you don't know what the indicator solution is reacting to in your tank. Is it the CO2? Is it the driftwood? Is it something else? With a standard solution, you know that the color-changing liquid (usually bromthymol blue, the same liquid used in most pH test kits) is reacting to the pH change caused by the introduction of CO2 and nothing else. It's the best way I know of to accurately check carbon dioxide levels in aquariums.
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post #3 of 12 (permalink) Old 02-12-2008, 11:22 PM Thread Starter
 
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thank you, I'll try that. I read I can make a 4dKH solution using distilled water and baking soda - is that right?
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post #4 of 12 (permalink) Old 02-12-2008, 11:37 PM
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thank you, I'll try that. I read I can make a 4dKH solution using distilled water and baking soda - is that right?
That's right.

I used billionzz's instructions to make my solution:
https://www.plantedtank.net/forums/ge...ndard-how.html

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post #5 of 12 (permalink) Old 02-12-2008, 11:43 PM
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It's pretty difficult to make an accurate solution without large volumes of water. Try to make a big batch.

pH and kH do not affect how much CO2 gets in your system. However, the amount of CO2 in your water does affect pH and kH readings.

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post #6 of 12 (permalink) Old 02-12-2008, 11:47 PM
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However, the amount of CO2 in your water does affect pH and kH readings.
Just the pH, the KH remains unchanged with regard to the level of CO2 in the water, thus that is the basis for how we determine the CO2 level itself; the change in pH relative to the unchanging KH.
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post #7 of 12 (permalink) Old 02-13-2008, 12:15 AM
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It's pretty difficult to make an accurate solution without large volumes of water. Try to make a big batch...
fishscale is correct.

billionzz's directions that I linked earlier starts with 3000 ml which is about 80% of a gallon of distilled water. 1 US gallon = 3785.4118 mL

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post #8 of 12 (permalink) Old 02-13-2008, 01:08 AM Thread Starter
 
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pH and kH do not affect how much CO2 gets in your system. However, the amount of CO2 in your water does affect pH and kH readings.
So, does this mean that, if I'm using a standard solution in my drop checker, I can just crank the CO2 until I get the color I want in the drop checker? And that, if I'm using a standard solution in the drop checker, that green=30ppm?

I just picked up some distilled water, a fresh box of baking soda, and also some epsom salts, because I figured they'd be useful at some point. My ferts arrived today, as mentioned. I ordered KNO3, KH2PO4, and Plantex CSM + B. I plan on using an EI dosing method.

With nothing added, my tap water chemistry, as per my home tests, is as follows:

pH 7.0
GH 80 ppm
KH 40 ppm
Fe 0.0 ppm
NO3 0 ppm
PO4 0.5 ppm

That's all I have test kits for (don't have a kit to test K, Ca, or Magenesium).

My fish are all soft water fishies, primarily SA fish, as previously mentioned, which is why I didn't bother ordering a GH booster - I quite like where my GH is.

Our most recent city water report is from '06. It lists specs as:

pH 7.6
GH 58.2
TDS 72
HCO3 60.9
NO3 0.21
Fe 0.006
Ca 20.34
Mg 1.7
K 1.143

Since suggested values for K are 20ppm, Mg is 5-10ppm, Ca 10-30, NO3 is 10-20ppm, I figure I should be dosing K, NO3, Mg, and Fe. Also, I figure it wouldn't hurt to boost my KH up a bit with some baking soda.

Am I on the right track here?
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post #9 of 12 (permalink) Old 02-13-2008, 03:23 PM
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Quote:
Originally Posted by chilligirl View Post
So, does this mean that, if I'm using a standard solution in my drop checker, I can just crank the CO2 until I get the color I want in the drop checker? And that, if I'm using a standard solution in the drop checker, that green=30ppm?

Also, I figure it wouldn't hurt to boost my KH up a bit with some baking soda.
Go easy on the CO2 in the beginning. The drop checker doesn't instantly read the changes in pH. In fact, it takes at least several hours. And yes, using a 4 dKH standard solution, green means 30 ppm, which is considered ideal for a planted aquarium. Some set theirs so it is green/yellow, which is closer to 40 ppm. But with fish, I'd be safe and keep it at 30 ppm.

As for your KH, I'd leave it as is. Your fish will adapt just fine. And you're asking for a lot of headaches trying to keep that value steady through water changes. Fish are much happier with steady and stable water conditions than what is considered optimal for them.
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post #10 of 12 (permalink) Old 02-14-2008, 02:51 AM Thread Starter
 
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Well, last night I added my ferts that came. I added 1 1/4 tsp KNO3, 1/2 tsp CSM + B, 5 tsp bkg soda, and 3 tsp epsom salts.

Tested my water today to see what effect it had. My pH went up to 7.2, KH is now 85ppm, GH is 100ppm, ammonia, trites, and trates all 0, Iron at 0.5.

Is it possible that after dosing KNO3 last night, my nitrates would be all the way back down to 0 today? Or is my test kit suspect? It's a good kit, liquid one by API, and has always worked in the past. The last time I got a positive reading for nitrates was a couple months ago, I was reading trace nitrates (more than 0 but less than 5), before I added live plants. The instant I added plants, those were gone. Are my plants just using that much food?

Is there a way to make a standard solution of KNO3 to test my test kit against? I'm sure there must be...off to read now...
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post #11 of 12 (permalink) Old 02-14-2008, 03:10 AM
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Quote:
Originally Posted by chilligirl View Post
Well, last night I added my ferts that came. I added 1 1/4 tsp KNO3, 1/2 tsp CSM + B, 5 tsp bkg soda, and 3 tsp epsom salts.

Tested my water today to see what effect it had. My pH went up to 7.2, KH is now 85ppm, GH is 100ppm, ammonia, trites, and trates all 0, Iron at 0.5.

Is it possible that after dosing KNO3 last night, my nitrates would be all the way back down to 0 today? Or is my test kit suspect? It's a good kit, liquid one by API, and has always worked in the past. The last time I got a positive reading for nitrates was a couple months ago, I was reading trace nitrates (more than 0 but less than 5), before I added live plants. The instant I added plants, those were gone. Are my plants just using that much food?

Is there a way to make a standard solution of KNO3 to test my test kit against? I'm sure there must be...off to read now...
Rex has a way to test your nitrate test kit with a known solution on his site here:http://www.rexgrigg.com/diy-reactor.htm#kit
Hope that helps,
John
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post #12 of 12 (permalink) Old 02-14-2008, 03:25 AM
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How to Make Reference NO3 and PO4 Solutions


Here's a way to make 10, 20, 30, 40 and 50 ppm NO3 reference solutions:

Note - This step requires that you have scales that can measure to 3 or more decimal places. Add 1.631 grams of KNO3 to 1 L distilled or DI water. This makes a 1000 ppm NO3 solution. (It's really a 1000.29 ppm NO3 solution.)

If you have scales that measure to one or two decimal places in grams; hereís two options. Omit the above step and start here:
Add 10.0 grams of KNO3 to 6.13 L of distilled or DI water or 5 grams to 3065 mL of distilled or DI water. This makes the 1000 ppm NO3 solution. (Itís really a 1000.49 ppm NO3 solution.)

Add 2 mL of the 1000 ppm solution to 18 mL of distilled or DI water. This makes 20 mL of a 100 ppm NO3 solution.

Add 15 mL of the 100 ppm solution to 15 mL of distilled or DI water. This makes 30 mL of a 50 ppm NO3 solution. You can use this for the 50 ppm NO3 reference solution.

To make a 10 ppm NO3 solution:
Add 2 mL of the 50 ppm solution to 8 mL of distilled or DI water. This makes 10 mL of a 10 ppm NO3 solution.

To make a 20 ppm NO3 solution:
Add 4 mL of the 50 ppm solution to 6 mL of distilled or DI water. This makes 10 mL of a 20 ppm NO3 solution.

To make a 30 ppm NO3 solution:
Add 6 mL of the 50 ppm solution to 4 mL of distilled or DI water. This makes 10 mL of a 30 ppm NO3 solution.

To make a 40 ppm NO3 solution:
Add 8 mL of the 50 ppm solution to 2 mL of distilled or DI water. This makes 10 mL of a 40 ppm NO3 solution.




Here's a way to make 0.1, 0.2, 0.5, 1.0, 2.0, 3.0, 4.0 and 5.0 ppm PO4 reference solutions:

Note - This step requires that you have scales that can measure to 3 or more decimal places. Add 1.433 g of KH2PO4 to 1 L of distilled or DI water. This makes the 1000 ppm PO4 solution. (It's really a 1000.09 ppm solution PO4.)

If you have scales that measure to one or two decimal places in grams; hereís two options. Omit the above step and start here:
Add 5.0 grams of KH2PO4 to 3.49 L of distilled or DI water or 2.5 grams of KH2PO4 to 1745 mL of distilled or DI water. This makes the 1000 ppm PO4 solution. (Itís really a 999.86 ppm PO4 solution.)

Add 1 mL of the 1000 ppm solution to 9 mL of distilled or DI water. This makes 10 mL of a 100 ppm PO4 solution.

Add 2 mL of the 100 ppm solution to 18 mL of distilled or DI water. This makes 20 mL of a 10 ppm PO4 solution.

To make a 0.1 ppm PO4 solution:
Add 1 mL of the 10 ppm solution to 99 mL of distilled or DI water. This makes 100 mL of a 0.1 ppm PO4 solution.

To make a 0.2 ppm PO4 solution:
Add 1 mL of the 10 ppm solution to 49 mL of distilled or DI water. This makes 50 mL of a 0.2 ppm PO4 solution.

To make a 0.5 ppm PO4 solution:
Add 1 mL of the 10 ppm solution to 19 mL of distilled or DI water. This makes 20 mL of a 0.5 ppm PO4 solution.

To make a 1.0 ppm PO4 solution:
Add 1 mL of the 10 ppm solution to 9 mL of distilled or DI water. This makes 10 mL of a 1.0 ppm PO4 solution.

To make a 2.0 ppm PO4 solution:
Add 2 mL of the 10 ppm solution to 8 mL of distilled or DI water. This makes 10 mL of a 2.0 ppm PO4 solution.

To make a 3.0 ppm PO4 solution:
Add 3 mL of the 10 ppm solution to 7 mL of distilled or DI water. This makes 10 mL of a 3.0 ppm PO4 solution.

To make a 4.0 ppm PO4 solution:
Add 4 mL of the 10 ppm solution to 6 mL of distilled or DI water. This makes 10 mL of a 4.0 ppm PO4 solution.

To make a 5.0 ppm PO4 solution:
Add 5 mL of the 10 ppm solution to 5 mL of distilled or DI water. This makes 10 mL of a 5.0 ppm PO4 solution.

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