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Drop Checkers - How They Work


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#1 aaronnorth

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Posted 02 January 2009 - 03:59 PM

Drop checkers – How they work

A lot of people have been asking various questions on Drop checkers, and it is quite hard to write up about them in a short answer, so here is a complete guide to the Drop checker.

A drop checker (or a permanent CO2 test) gives us a constant reading of the CO2 levels in the tank.

We fill the drop checker with either 4dkh, or 5dkh solution (4dkh being the more popular), and add 3 drops of bromothymol blue (Blue liquid which can be found in low range ph test kits). It is important that you use 4dkh or 5dkh solution, DO NOT use aquarium water, as this contains other acidic substances, which can affect the reading (hence why the ph/ kh CO2 tables are inaccurate!)
As the CO2 gasses off from the aquarium into the drop checker, the ph lowers due to the carbonic acids formed by CO2 when it dissolves in water. When the drop checker turns from blue, to green, this indicates a pH of 6.6, and because we know the solution is 4dkh, this tells us we have approximately 30ppm of CO2 in our tank water.
If you are using a 5dkh reference solution, then a pH 6.6 (green drop checker) will indicate 38ppm.

4dkh reference solution is available from here
Bromothymol blue can be found here
A cheap Drop Checker is available from here

Size, shape, price whatever does not affect the performance of a drop checker. And as you can see with the one above it comes supplied with bromothymol blue.

The 4dkh solution may look as though it is expensive, but with the pictures below, I used 1ml to get half the ball full! So changing that weekly will last me 500 weeks/ 9 years (£1.11 per year!) Obviously some drop checkers are larger than others. You can change the solution every few weeks if you like, but I prefer to do it weekly.
If you want, you can always make your own reference, but make sure you have accurate scales (0.01g) and use very accurate measurments:

Add 6g of pure Sodium Bicarbonate to 5l of DeIonised water (DI) to give you a solution at 40dKH.

Mix 100ml of this solution with 900ml of 'fresh' DI to give you 1l of 4dKH reference solution.

This obviously makes a lot, so you can sell some on (providing it is accurate).
You can scale this down; add 1.2g for every 1L of DI water, as this will always give you 40dkh
You always mix 100ml of this solution with 900ml of 'fresh' DI, as this is a 1 in 10 dilution, it will give you 4dkh.

I wouldn't go smaller than 1L as you could risk making the solution innacurate,

DI water is available from the car section at Halfords,

Firstly, turn your drop checker upside down, and add 2 or 3 drops of bromothymol blue (the more reagent you add, the darker the colour)

Then squirt a small amount of dKH reference solution into your drop checker

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Tilt it slightly so it runs into the ball, and pushes the air out (can take a little practice), hopefully you can see the air bubble escaping in this picture.
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Turn the drop checker back over, and insert into the aquarium, making sure there is an air gap. Note the colour should be blue.
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Try to fill the ball half full, as this ensures the maximum surface area for gaseous exchange, and therefore a quicker reading. Here is the colour recomended (lime green).
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A blue colour indicates you have low CO2 (25ppm or less)
A green colour indicates your CO2 levels are ok (26 – 35ppm)
A yellow colour indicates the CO2levels are too high (36ppm or more)

Aim for a lighter/ lime green colour, as this ensures you have enough CO2.

Note: The colours in a drop checker take on average 2 hours to change colour, so be patient and adjust the levels slowly, as some people put the levels up high as they are worried they are not injecting enough, only to find they have gassed their fish.

E.g. A green drop checker at 3.00pm means that the level of CO2 was 30ppm at 1.00pm. So the levels may be slightly higher by this time.

Here is a picture kindly submitted by Supercoley1 showing the reaction times of 2 different types of drop checkers (tear drop left, chameleon right)
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11am, fresh solution inside the drop checker.
3pm, CO2 starts
4pm, lights on with CO2 being injected for a total of 1 hour.

Start injecting the CO2 up to two hours before lights on, to make sure the levels have built up, and turn it off, up to 3 hours before lights off because the levels will remain high enough for plants, as they slow down their photosynthesis rates towards the end of the day.

Edited by aaronnorth, 06 March 2011 - 07:35 PM.


#2 RadaR

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Posted 02 January 2009 - 09:20 PM

Good guide, mate. If it were pinned then it would be easy to refer it to newbies :)
Of course, that's a mod's decision.

#3 Truck

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Posted 02 January 2009 - 09:24 PM

Pin :good:

#4 chr15_8

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Posted 02 January 2009 - 09:34 PM

have to agree would make a good sticky.

great post btw

#5 aaronnorth

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Posted 03 January 2009 - 10:56 AM

Thanks for the comments :)

#6 kcharley

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Posted 03 January 2009 - 03:19 PM

Thanks Aaron. Great timing also. This the one part I haven't ordered yet. Thanks again.

#7 Jaymz

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Posted 04 January 2009 - 04:50 PM

Excellent advice as always, deserves to be pinned.

#8 fish.com1

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Posted 07 January 2009 - 08:53 PM

Great guide. Should be pinned.

#9 waterdrop

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Posted 07 January 2009 - 11:04 PM

Wow, really interesting!

As a newbie, I'm getting the idea that drop checkers are really better to use than those expensive pH feedback controller things. Is that true?

~~waterdrop~~

#10 Thommo

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Posted 08 January 2009 - 11:11 AM

WOW :hyper:

How ironic. My drop checker arrive and I just put it in but was wondering how it all worked.

Great advice for a Newbie like myself. Please Pin

#11 SuperColey1

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Posted 08 January 2009 - 11:21 AM

Wow, really interesting!

As a newbie, I'm getting the idea that drop checkers are really better to use than those expensive pH feedback controller things. Is that true?

~~waterdrop~~


There are arguments betwen people within the hobby over the Ph controllers. Basically the manufacturers spiel loads of gubbins r.e. controlling CO2 with these rather than actually doing some research. Some people use them but not many.

The most important thing about CO2 is stability. Meaning that you want to maintain a reasonably consistent level of CO2 within the water. If we aim for 30ppm then we don't want it going 15-30-15-30 all day long as the plants adapt themselves to the CO2 level available. If they have to keep adapting they can't grow while they are doing this adapting and so algae jumps in.

Using a Ph controller (like using tank water in the drop checker) is assuming that the Ph level is all down to CO2 and ignoring other factors. Therefore when set to turn the CO2 off at 1ph lower than the normal ph it is assuming that the 1ppm drop is down to the CO2 where it may be other acids etc that are partly the cause. These are natural acids which are in every tank etc.

Therefore what most planted people suggest is if you already have it and want to keep it then set it much lower 1.2-1.5ph below normal so it does NOT control the CO2 injection. You want the CO2 to keep running. It will however act as a safety measure and switch the CO2 off if there is a severe problem and avoid a 'Ph crash'. This can be the case sometimes when a bottle is almost empty as the pressure drops significantly and then some regulators/needle valves cannot deal with the reduced pressure and let the remainder of the cylinder 'dump'.

Summary - Save your money. A 5 drop checker will let you see the levels. You can get it setup to a good level over a few days, instantly see if it needs upping as the plantmass increases. Instantly see yellow and turn the CO2 off etc. Spend the money on better circulation and/or plants

AC

#12 aaronnorth

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Posted 08 January 2009 - 04:24 PM

Wow, really interesting!

As a newbie, I'm getting the idea that drop checkers are really better to use than those expensive pH feedback controller things. Is that true?

~~waterdrop~~


Rather than carbonic acids produced by CO2 that lower the pH, other acids are also in the water column such as humic acid, nitric acid etc. These all contribute to the lowering of the pH, so therfore the pH can be lowered, and stay at that level, so no more CO2 will be injected and plants will starve!

#13 bordercollie05

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Posted 08 January 2009 - 09:33 PM

I've seen a DIY drop checker you can make from a baby food jar (or similar) and a funnel. You just get the smallest funnel you can find and put it in the top of the jar, then glue together and turn the whole thing upside down (so the solution is in the lower half or so of the container...the funnel allows water in but no solution out). Not sure how you suspend it in the tank though....


Great article aaron!

#14 aaronnorth

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Posted 09 January 2009 - 07:03 PM

I've seen a DIY drop checker you can make from a baby food jar (or similar) and a funnel. You just get the smallest funnel you can find and put it in the top of the jar, then glue together and turn the whole thing upside down (so the solution is in the lower half or so of the container...the funnel allows water in but no solution out). Not sure how you suspend it in the tank though....


Great article aaron!


Thanks, for anyone interested in making a DIY drop checker, here is a video, although i would rather spend 5 than waste my time on that ;)

How to make a DIY drop checker

#15 Carter

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Posted 03 February 2009 - 11:01 PM

thanks for the post dude, helped me out a lot.


I'll have to go down to the shop today and ask them to order in some of this stuff.

#16 keenonfish

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Posted 05 February 2009 - 10:55 PM

Hey thanks for the post this should be pinned! I am tempted to make my own 4dkh but couple of questions... Where do I get DeIonised water from (ironing / car battery water?) and I assume the stuff doesn't deteriorate over time?

#17 Truck

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Posted 05 February 2009 - 10:56 PM

Hey thanks for the post this should be pinned! I am tempted to make my own 4dkh but couple of questions... Where do I get DeIonised water from (ironing / car battery water?) and I assume the stuff doesn't deteriorate over time?



halfords, you normally use it for car batteries

#18 keenonfish

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Posted 05 February 2009 - 11:11 PM

Hey thanks for the post this should be pinned! I am tempted to make my own 4dkh but couple of questions... Where do I get DeIonised water from (ironing / car battery water?) and I assume the stuff doesn't deteriorate over time?



halfords, you normally use it for car batteries


ok thanks I thought as much but thought I would check. So the mixture should last then?

#19 Truck

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Posted 05 February 2009 - 11:13 PM

im not sure

i would have thought so

Edited by truckasauras123, 05 February 2009 - 11:13 PM.


#20 SuperColey1

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Posted 06 February 2009 - 07:47 AM

As long as the bottle is closed then it will only deteriorate minimally so not enough to worry about.

DI water is readily available at Halfords, Wilko, Boyes etc

AC




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