How to make a reference KH solution for CO2 measurement

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So I've been using the RedSea drop checker with a 4 degree KH solution and double the amount of pH reagent to make the color easier to read.

I've had a wierd result that made me think the test had been affected in some way (say some tank water got in the checker or the hole was clogged), because after putting the checker in the tank it failed to ever turn BACK blue after going green. I thought this was odd because I would assume it should go back pretty readily after the CO2 goes off (off at 10pm and not back on until 12pm the next day).

So thinking the checker solution was bad I took it out of the tank and set it on my desk. I came back a couple hours later and it was dark blue!

I'm wondering if the amount of plants I have in the tank are keeping the dissolved CO2 levels at/above 30ppm when I'm not injecting any CO2?

I've double checked the solution and it indeed takes exactly 4 drops of KH solution for the change and I made it on the large 5L scale as in the OP.

And for anyone else trying this out here's my recommendation (especially if using the Red Sea checker):

1. Place it in a place where you can EASILY see the color change. I had originally had it dead center in the tank on the front glass so it was in an even spot in the tank (so I wouldn't see overly high or low levels due to my mist PH dispersion). That was great except I couldn't ever get a reading because looking through the checker was looking into my plants! (surprise they are green :) ). What I did was put it near the upper left corner so I can look down through the tank against the white plastic and it allows me to guage the color (and its far away from the PH so I don't feel I'm reading elevated levels).

2. Tilt the checker once its below the water line to get the majority of the bubble out of the opening. The larger this gas layer, the slower your checker will change. I look carefully from the bottom of the tank and tilt just enough to get a big bubble out. There is still a small bubble underneath, but it should respond much faster than if you just placed it in the tank. Definitely don't tilt it enough to allow spillage of the solution into the water as you will contaminate your tank (probably not that serious), but you also risk contaminating the fluid in the drop checker and invalidating your results.
 
In my 5g, I had an "open type" checker go yellow on me, I mounted it outside the tank. It stayed yellow for 3-4 days, then went back to green, still hasn't gone blue.... I thought that maybe some acetic acid residue from the silicone used to assemble it had found its way in. I'm going to keep it in the air & see if it ever goes blue.
 
A COUPLE OF IMPORTANT CHANGES.

Please be aware if you are going to make a reference solution, there have been a couple of changes to the measurement and proceedure that have been reconsiled in the last few days.

First is that you will want to mix 6.00g of Baking Soda, not 4.99g in your 5 liters of distilled water.

Next is that you do not want to bake the baking soda, as this can apparently change the properties if the compound.

With those two adjustments you should be good to go. Good news is, both of those make the process even easier. I should go back in my picture thread and add in these changes...

See this thread for details on these changes (page 2):

http://www.barrreport.com/articles/2630-making-standard-kh-solutions.html
 
OK - having read some of the 2/2 posts, I'm now getting (baking soda on an anhydrous basis)...

4dKh = 1.43mEQ/L = 0.715mM CO3¯ ¯
1L*0.715mM*84mg/mmole=60.06mg baking soda per Liter 4dKH solution

6g/5L=28.57meq or 80dKH, dilute 10mL to 200mL for 4dKH (again, all assuming anhydrous baking soda).

I guess I'll have to do a Karl Fischer titration on a sample of the baking soda I have first, divide my intended weight of baking soda by my % baking soda (100%-%water).

Maybe this explains why I've always seen either green or yellow in my drop checkers.

Helpful reference: http://ozreef.org/library/tables/alkalinity_conversion.html
 
I just have to let you guys know that I just received a lab certified analytical standard of 4 dKH from billionzz. It cost a little more then 10 bucks shipped and I am very happy with the product. He has baking soda standards of 4 and 5 dKH along with the lab certified ones diluted using class A glassware and Demin water.

Very professional transaction. I am adding this here so others who are looking for this will be able to find it. Just Google "billionzz" and you will find him.

kh.jpg


EDIT: He now has a site setup for the KH standards:

http://liquidarthome.net/khstandard
 
4dKh = 1.43mEQ/L = 0.715mM CO3¯ ¯
1L*0.715mM*84mg/mmole=60.06mg baking soda per Liter 4dKH solution

6g/5L=28.57meq or 80dKH, dilute 10mL to 200mL for 4dKH (again, all assuming anhydrous baking soda).

I guess I'll have to do a Karl Fischer titration on a sample of the baking soda I have first, divide my intended weight of baking soda by my % baking soda (100%-%water).

Ahhhh... what? What language are you speaking? :lol:

This sounds like a very time consuming process, at least in mixing the solutions, which sounds as if is 90% of the work. I was just getting used to the system people on APC came up with of just turning your C02 down when your fish start gasping for air!

Could someone translate this whole process from begining to end in simple terms, "Drop checker C02 measurement for Dummies," for the ignorant working class people like myself, and then I can pass it along to my legions. I don't even know what a drop checker is, sorry! I never used one. A few years back, Cathy Hartland wrote a nice translation of the Sears and Conlin PMDD for me. I miss Cathy! Can someone take pity on me and write such a step by step instruction for my puny little mind? :wink:

Robert Hudson
www.aquabotanic.com
Read my column in FAMA magazine
"The Planted Tank"!
 
The concept of a drop checker is very simple and elegant. You do a pH test with your favorite pH test kit (normal, not high, pH test range) using your aquarium water. Now, instead of throwing the test solution away, pour it in your drop checker and put your drop checker in your tank.

Whatever style drop checker you use, they all work on the same concept. You have your test solution separated by an air gap and on the other side of that air gap is your tank water.

Now... we all understand that if you can get your pH and kH, you can find a chart that will tell you how much CO2 you have in your tank. Well, the only difference between the test water in the drop checker and your aquarium water is the CO2 level (and the pH regent I guess, but we won't worry about that). As it happens, the CO2 passes through the air gap from your aquarium into the drop checker and over a period of time, say 1-2 hours, equalized with the liquid in the drop checker. So as your pH goes up or down (assuming you are inject CO2 somehow) the color of the liquid in the drop checker will confirm this change in pH.

So, now that you understand how a drop checker works you can start picking it apart. There are many other factors in your aquarium water that can change your pH and kH besides CO2 injection (think Aqua Soil, Phospate Dosing, etc)... Also the ideal color of the pH test solution really depends on what your tank kH is.

In step our use of a reference solution. Instead of putting tank water in your pH test, use a lab certified (or mix up your own) solution of distilled water and kH. Using a 4dKh reference solution for example, gives you an ambient 7.6pH with distilled water. In your pH test this will show up blue. Put it in your tank, which most likely has a different pH and kH, and let the CO2 equalize across the air gap into your reference solution and now you have a much better measure of CO2. Using the 4dKh reference example, once your pH in the Drop checker reaches 6.6pH, referring to the pH/kH chart, you have 30ppm of CO2. As it happens (not by any mistake) your pH test kit turns GREEN at 6.6pH. If you keep adding more CO2, the liquid will turn yellowish, if CO2 decreases in your tank, the drop checker will turn blueish...

Using a reference solution you remove all variables that could change pH/kH except CO2, making it a much more accurate way of measuring and monitoring your CO2.

I use mine with a fully automated system for a few reasons: (1) after you use a pH meter for a period of time you will start to see it become inaccurate and require frequent calibration. It is also only measuring pH and you are assuming that your kH is what it was last time you tested (not always a safe assumption. (2) your pH meter will not scream at you or otherwise let you know if your CO2 tank is out of gas, your solenoid is stuck open or shut, etc. On more than one occasion my Drop checker has been my first indication that my CO2 had run out.

I could go on, but this is already a lot longer than I had planned... I hope this helps a bit.
 
About a month ago I installed a Red Sea CO2 Indicator (drop checker) in each of my three tanks being injected with CO2. Works like a dream. Just refilled with fresh solution today. I found that the manufacturer recommended amounts for the mix ended up being a bit hard to read, so I modified it slightly this month and it's much more readable.

Manufacturer Recommendation
1ml of tank water (obviously substitute chosen KH reference solution)
2 drops indicator solution

Modified mix
1.5ml of KH reference solution
4 drops indicator solution

You can just barely still get the indicator rotated after filling with this much solution. The results are a darker color that is easier to see without turning muddy.
 
^ I bought the Red Sea today, cant wait to get it working

Does anyone know if its OK to substitute DI water with RO water for making the reference solution?
 
Just wanted to ask how the indicator works as a function of air gap. I normally try to fill up the Red Sea unit with my 4 degree KH solution and 6 drops of pH indicator leaving as little air as possible. Would it react faster if I had less liquid and more air? I also remove most of the air underneath the Red Sea unit by tilting it sideways to let the large bubble out.
 
I have heard that putting LESS kH solution in the drop checker will help it equalize faster. So instead of filling it all the way, fill it like half way. Reducing the air gap may also help, but I think the biggest savings is in reducing the quantity of liquid in the drop checker.

I will let someone else perhaps reply with more details on why this is so.
 
dapellegrini said:
I have heard that putting LESS kH solution in the drop checker will help it equalize faster. So instead of filling it all the way, fill it like half way. Reducing the air gap may also help, but I think the biggest savings is in reducing the quantity of liquid in the drop checker.

I will let someone else perhaps reply with more details on why this is so.

Thanks for the reply. I think I'll be trying this out in the near future. Right now it seems to take FOREVER to get a change and it isn't always back to "normal" in the morning even though the CO2 has been off since 11pm the night before (7-8hours).
 
I have also heard that some non-glass drop checkers can leak tank water into the test solution. The one-piece glass ones will definitely not do this to you.
 
7Enigma said:
Thanks for the reply. I think I'll be trying this out in the near future. Right now it seems to take FOREVER to get a change and it isn't always back to "normal" in the morning even though the CO2 has been off since 11pm the night before (7-8hours).

Mine do the same thing, but how do you know that the fish tank is really at it's 'normal' CO2 level in the morning?

During PWC's, my drop checkers go blue and within an hour of refilling the tanks, the solution is back to green. This indicates to me that the drop checker (rea sea one) is working properly and has a reaction time of about an hour. And just like yours, mine remain green all night long.

I would have to say that my CO2 is staying around 30 PPM during the night cycle. We (planted guys) have a lot of plants in our tanks adding CO2 to the water column at night (let alone the fish). How much CO2 is added by plants? I have no idea, but I do know that my CO2 system is off and I can maintain ~30PPM CO2 during the night.
 
if drop checker changes colour from blue to green when co2 at right level in tank why put 4 kh souluton in it if tank water is 5 kh ? wont that give me false reading?
 
The point of the drop checker is to remove the variables of aquarium water. While your tank water may be 5 dKH, what if there are other variables that throw off the pH/KH relationship? Further what if something happens that slowly changes your pH/KH other than the CO2 injection that you don't notice? Further many people don't have water with dKH within the range that allows green to be an indication of 30ppm of CO2. With a KH of 5 dKH your indicator is actually showing higher than 30ppm CO2 when it turns green. While it's still a good number and not so high as to cause problems, it isn't 30ppm. By using the reference solution you remove these variables.
 
tnks purrbox i think i finally understand will try and make some to use also ..I just checked my ph and kh and showed around 15 ppm but drop checker shows very light green colour almost yellow.
 
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