# Recycled drop checker...



## Henrik (10 Dec 2008)

I have an old drop checker from sera, but ran out of the liquid many years ago. Can I use a simple PH test liquid (Tetra? Sera?) and re-use the DC?  It says in the instructions that you fill it with tank water and then put 3-4 drops in...

I have read that people use a KH4 liquid instead of tank water, but my tank water is actually KH4, so do I need to bother about spending money on a KH4 standard?

Thanks, Henrik


----------



## scottturnbull (10 Dec 2008)

You don't need much 4 dKH. And it isn't all that expensive. You can even make your own, with a decent KH test kit, DI water, and Sodium Bicarbonate. I recommend the Salifert KH test kit. I tested the 4 dKH water from AE and it was fairly accurate (that, or they use the same kit to mix the water).

The PH test kit must have Bromothymol Blue indicator. API PH test kit (range 6-7.6) uses it. So does the Hagen PH low range test kit. The amount of indicator used will depend on how much fluid the drop checker holds. Adding the wrong amount just makes the colour paler or more intense.


----------



## GreenNeedle (10 Dec 2008)

Although your tank water may be 4dKH this is not the only reason we use 4dKH either homemade or bought.  the 4dKH we buy or make will be pure DI water with just the right amount of bicarb added.

Your 4dKH tank water may have all sorts of different things in it which could 'sway' the reading!!!

Are you saying from using the Salifert test on the AE 4dKH that the solution is fairly acurate or that the test is? 

AE don't use a Salifert test kit to mix the solution  I can guarantee!!!  It is laboratory tested.

AC


----------



## scottturnbull (10 Dec 2008)

SuperColey1 said:
			
		

> Are you saying from using the Salifert test on the AE 4dKH that the solution is fairly acurate or that the test is?



I'm not sure, either.

I'm loath to correct it. The ambiguity appears meaningful. Whether it was the test kit or the solution that was fairly accurate, I don't know.

The test kit claims a 0.3 +/- dKH accuracy. The 4 dKH water claims to be accurate to 0.01 ppm. Perhaps that helps.


----------



## Henrik (10 Dec 2008)

By how much can a different KH 'sway' the result - as the instructions on the sera kit actually tell you to use your tank water whatever its KH!


----------



## aaronnorth (10 Dec 2008)

Henrik said:
			
		

> By how much can a different KH 'sway' the result - as the instructions on the sera kit actually tell you to use your tank water whatever its KH!



quite a lot, other acids in the water affect the results - one of the reasons why the kh/ ph co2 tables are innacurate.


----------



## GreenNeedle (10 Dec 2008)

I don't think that many test kits are too far out in their result, more the interpretation of the result can be vary from user to user.

When trying to adjudge a variety of slightly different colours of liquid against solid colours on a white card can give a huge difference in readings for the same sample between different users.  This is the same with the tabs.  Judging a wet mushy reading against the solid colour on the container is nigh on impossible to call accurate.

I never said a DIFFERENT Kh could sway the result (although a different Kh WOULD definately sway the result.)  I said using 4KH tank water could sway the result. 

What I was trying to point out is there is a difference between a known 4dKH reference solution where you know there are no other contaminants and a tank water sample that is 4KH that contains all sorts of other contaminants.

All the drop checkers say to use tank water but does anyone go by this?  No because we have learnt it is better to use a known reference rather than letting the possibility of contaminant swaying the result occur.

Just a note about using different Kh.  If you were to take 10ml of the 4dKH solution and mix it with 10ml DI you now have 2dKH solution.  This should now turn green at approx 15ppm!!!! (Remember I am no scientist nor wish to be)

AC


----------



## Ed Seeley (10 Dec 2008)

4dKH water gives a green colour (pH of 6.5) with 30ppm CO2.
3dKH water gives a green colour with 22.5ppm CO2.
2dKH water gives a green colour with 15ppm CO2.

When I used DIY CO2 on my nano tank I used a 2dKH drop checker solution and would change the yeast mix when it changed from yellow or green.  

IMHO GH and KH test kits are pretty accurate as they rely on a known reaction.  As Andy says I think it's usually the interpretation that causes inaccuracies or poor usage.  If you make sure you are using proper drops (by making sure the liquid dropper is vertical not at an angle), that you've accurately measured the water volume and using a white piece of card to accurately gauge the colour and that will go a long way to improving the accuracy.

You can improve the accuracy of the GH and KH test kits by doubling the water volume which means each drop measures to 1/2 degree rather than 1.  Double it again and you get 1/4 degree.


----------



## Henrik (11 Dec 2008)

How do the drop checkers work anyway - I take some calibrated KH4 liquid, add blue ph testing liquid, and then turn it upside down or in some other way seperate this testing liquid from the tank water. How does the colour change then work?


----------



## Henrik (11 Dec 2008)

SuperColey1 said:
			
		

> What I was trying to point out is there is a difference between a known 4dKH reference solution where you know there are no other contaminants and a tank water sample that is 4KH that contains all sorts of other contaminants.



Another thing - does that mean that using tank water in a drop checker gives you the same (inaccurate) result that a ph/KH table will give you? Given that I know my KH and ph, would this mean that I am no better off with a DC than a ph/KH table unless I use properly calibrated KH4 solution?

This is just to really understand the context - I am already clear that I HAVE to calibrate a clean KH4 solution :!:


----------



## Egmel (11 Dec 2008)

Henrik said:
			
		

> How do the drop checkers work anyway - I take some calibrated KH4 liquid, add blue ph testing liquid, and then turn it upside down or in some other way seperate this testing liquid from the tank water. How does the colour change then work?


They work by gas exchange, at the beginning the tank water gives off CO2 and the Drop checker test solution takes in CO2, as the amount of CO2 in the test solution increases to the same level as that in the tank water the system reaches equilibrium.  This is why there is a delay in the drop checker reading since it takes a while for the CO2 to saturate the test solution fully.

The Barr report has a nice explanation.


----------



## ceg4048 (11 Dec 2008)

Some useful info can also be found in the Tutorials thread CO2 MEASUREMENT USING A DROP CHECKER

Cheers,


----------



## Henrik (11 Dec 2008)

Thanks, very clear. I actually produce 4dkH clean water every week for my tank using some potassium bicarbonate, but there is some phosphate in the water. Hand on heart - how wrong would I be using this water in the drop checker? It would save me fiddling around with miniscule amounts of bicarbonate in distilled water, or spend Â£10 plus postage on a dKH4 bottle...
Thanks, Henrik


----------



## Egmel (11 Dec 2008)

Henrik said:
			
		

> Thanks, very clear. I actually produce 4dkH clean water every week for my tank using some potassium bicarbonate, but there is some phosphate in the water. Hand on heart - how wrong would I be using this water in the drop checker? It would save me fiddling around with miniscule amounts of bicarbonate in distilled water, or spend Â£10 plus postage on a dKH4 bottle...
> Thanks, Henrik


I'm not sure on how much it would alter the reading but you're right the cost of the 4 kdh water has gone up (it's a bigger bottle than they used to do) the alternatives are an all in one solution or make your own using distilled water which will be cheaper to buy and you can probably get locally.


----------

