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Drop checker stopped working

Sacha

Sacha

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Joined
3 Jan 2014
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992
Location
London
I use Co2 art 4dKH water with 5 drops of Bromothymol blue from the API pH test kit bottle.

This has been working fine for a few months. But now the drop checker has stopped working. It is always yellow in the tank. When I take it out of the tank, it turns blue after a couple of hours. However in the tank, it is always bright yellow, even when the Co2 has been off and there has been serious surface agitation for 24 hours.

Please don't reply saying "if it turns blue out of the tank it must be working", because I guarantee it isn't. The Co2 concentration in the tank right now is less than 10 PPM, but the DC is bright yellow.

It's not contaminated- I have cleaned it thoroughly with hydrogen peroxide several times.

Can someone recommend a 4dKH/ Bromo Blue combination that is 100% reliable? Because I have had a lot of trouble with 4dKH in the past, I have bought several bottles of crap that doesn't work.

Thanks a lot.
 
Aquaessentials sell 4dkh Bromothymol blue solution already pre-mixed.

Drop checkers are over rated any way, there not very accurate and only show you what was happening in the tank two hours earlier. I would just monitor your pH profile. That will tell you for definite if you are injecting enough co2 or not.
 
I bought that pre- mixed solution from AE a while ago. I threw it in the bin because it didn't work. The fluid was clear, as clear as water. Always. It never showed any colour. That's the only time I've been disappointed with them.

I do monitor my pH profile. But I want a drop checker as well, as an alarm if anything is not right. I can't be doing pH profiles every day.
 
Sacha said:
I bought that pre- mixed solution from AE a while ago. I threw it in the bin because it didn't work. The fluid was clear, as clear as water. Always. It never showed any colour. That's the only time I've been disappointed with them.

I do monitor my pH profile. But I want a drop checker as well, as an alarm if anything is not right. I can't be doing pH profiles every day.
Click to expand...

Monitor your fish and plants, they will tell you if any things is wrong. :)
 
It was ages ago. They definitely sent me the right bottle. Must have been messed up on the production line. Before I threw it away, I tried treating it as 4dKH by adding Bromo Blue separately. That didn't work either- it just turned yellow permanently.

It was £5 about a year ago, I'm not too bothered now.
 
Hi Sacha,

I use the premixed solution from AE and as has been said, it shouldn't be clear. It's premixed and therefore blue, quite dark blue actually. If yours was clear it appears they sent the wrong solution.

I feel sure if you get the right stuff from AE you will be pleased with it.

Of course it is very unlikely the drop checker stopped working, rather the drop checker fluid, as the drop checker itself is but a vessel for holding the reagent away from the tank water allowing only CO2 to transfer from tank to reagent.

Harry.
 
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I understand what you mean about the drop checker "not working" as I have drop checkers in two tanks with the same solution in them both (4dkh and 5 drops bromo blue from CO2 art) - one of them seems to work ok, whereas the other is permanently blue, despite me injecting through an inline diffuser at an uncountable bubble rate just under what makes the fish sit at the surface. I have given up on mine really and just use it for decoration haha.
 
Im In the same boat. Ive given up with it tbh. Ive done a ph profile and im happy with it. Ill just use the fish for reference now.

Sent from my GT-I9300 using Tapatalk
 
It's just so puzzling. I changed the drop checker indicator fluid yesterday. I left it out of the tank for several hours and it was very dark blue. Then I put it in the tank, and a couple of hours later, it turned bright yellow, and it is still bright yellow now, even though Co2 levels are very low..
 
Hi all
Sacha said:
Then I put it in the tank, and a couple of hours later, it turned bright yellow, and it is still bright yellow now, even though Co2 levels are very low..
Click to expand...
It is possibly because the "Bromothymol blue" doesn't measure CO2 as such, it is just a narrow range pH indicator <Bromothymol blue - Wikipedia, the free encyclopedia>. For whatever reason the solution inside your drop checker is now acidic.

You can use a drop checker with 4dKH "water", because of the experimentally defined relationship between CO2, pH and carbonate hardness.

ph-kh.jpg


When you dissolve CO2 in water a very small proportion of it goes into solution as "carbonic acid" (H2CO3), normally this only has an effect in depressing the pH in water without carbonate buffering (bi carbonate is HCO3-, and H+ is the acid), because of the carbonate~CO2 equilibrium:
655959a52b2ae8f4893e12716bf4a86c.png

When you continually add CO2 the pH falls, and when you stop adding CO2 the pH value returns to equilibrium. How far the pH falls, and what your original pH is depends upon the reserve of HCO3- (a base is a "H+ ion acceptor").

The drop checker has an "air gap", this should ensure that only the CO2 coming out of solution from the tank water, and re-entering solution in the drop-checker, is measured by the pH change.

cheers Darrel
 

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Thanks for that Darrel.

Any ideas as to why the solution in the DC is now acidic?
 
You do need to replace the fluid from time to time. Bromothymol blue is sensitive to light, which is why you should store your stock solution in the dark.
I think my pre mixed solution is from AE and it works fine, and as HarryH says, it should be dark blue.
I suppose it is possible that the indicator has become degraded and the reaction curve steepened, so it changes colour at a higher pH??
In which case you need to get some new stuff.
Failing that, acid is getting into your drop checker, no other explanation.
If it is not CO2 (it is the only gas that will affect pH), then it must be directly from the tank water. What is the pH of your water?
 
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