# Drop checker Staying Yellow even with CO2 switched off



## markl (29 Apr 2013)

Hi All,
I'm a bit confused, I set up a new system on Saturday. 538 litres, FE Co2, 216w T5 lighting.
I planted the tank, not really densely but an average amount of various potted plants (£70 at my LFS)
I am relatively new at planted tanks, but i'm confused whats happening with my CO2 levels.
I set up the FE on the first day of planting, I'm using x2 basic diffusers, going underneath my x2 external canister filter inlets at each end of the tank.
After the Co2 had been running for several hours - about 6 hours the drop checker turned really yellow. I turned down the CO2 to what I thought was an appropriate level prob about 3-4 bubbles a second and had a tinker. Anyway long story short - CO2 got switched off last night and when I came down this morning the drop checker was still yellow - I never turned on the CO2, but I did replenish the liguid in the checker for some fresh blue and then went to work - still no CO2 switched on but lights on.
When I have returned home from work this evening the drop checker is still yellow with no CO2 switched on - I'm confused, does anyone have any reasoning for this?
Many Thanks
Mark


----------



## Steve Smith (29 Apr 2013)

Are you using 4dKH water with the indicator fluid or tap/tank water?  If the latter, that would affect the drop checker and not give an accurate reading.


----------



## markl (30 Apr 2013)

I am using ore mixed waterlife solution, no tap/tank water


----------



## John S (30 Apr 2013)

If you take the drop checker out for a while does it return to blue?


----------



## markl (30 Apr 2013)

Hi
Last night, I took the original solution out and put it in a pint of water - this morning that solution has only just started to turn blue - as i speak the solution is a greeny/blue colour.

Last night i put some new (different solution) in a new DC in the tank - this morning that solution is green in colour. I still have not switched the CO2 on.

How can this be possible?, there has been no CO2 switch on for 36 hours now - I'm proper confused?!

My substrate is a black quartz gravel over a 1cm layer of Tropica Plant Growth Substrate - would that be making any difference?

I am on day 4 of having the tank filled, so i was thinking of coming home from work and doing a 50% water change, wash out the DC's and try again - any other ideas/explanations for this?

Many Thanks
Mark


----------



## faizal (30 Apr 2013)

My guess is there's something wrong with the solution. What is ore mixed water life solution?


----------



## ian_m (30 Apr 2013)

Some drop checkers & solution are meant to be used with tank water. The older JBL model is one for instance. Bit pants really as you are supposed to compensate the drop checker colour against KH of your water. Mine was a couple of quid 2nd hand on Ebay.

If you put the older style JBL solution into the drop checker either undiluted or diluted with deionised water it is goes yellow and stays yellow regardless of CO2 levels.

If you put the older style JBL solution into the drop checker diluted with tank water it is goes blue starts heading to green when CO2 is on.

The newer style JBL drop checkers have the following quote "The new JBL CO2 Permanent + pH Test Set uses an indicator which is ready for use and does not need to be diluted with aquarium water."


----------



## dw1305 (30 Apr 2013)

Hi all,
It is probably because of the pH of the tank water, before you add any CO2. The liquid that changes colour in the drop checker is just a narrow range pH indicator (bromothymol blue). Below pH6 bromothymol blue is yellow, and above pH7.6 it is blue. It will change colour to reflect the pH of the water.

We can use a drop checker to estimate CO2 levels, because adding CO2 drives the carbonate ~ CO2 equilibrium towards the acid pH range. This happens because a small proportion of the added CO2 dissolves as carbonic acid (H2CO3), and this acid lowers the pH. The amount of CO2 you need to add is dependent upon the carbonate buffering of the tank water.

This relationship between carbonate buffering (dKH) and CO2 is shown in this chart, from the "sticky": <CO2 MEASUREMENT USING A DROP CHECKER | UK Aquatic Plant Society>:





cheers Darrel


----------



## markl (30 Apr 2013)

Many thanks for your help all, 

Darrel I understand some of what you are saying, but I've just checked the ph and it is 7.6


----------



## dw1305 (1 May 2013)

Hi all,


markl said:


> but I've just checked the ph and it is 7.6


I'd definitely try some new indicator, but do you have a measure of the dKH? if you use tap water you should be able to get one from your water company.

The problem with pH is that it is a ratio, and doesn't tell you anything about amounts. The water companies add NaOH to the water supply (to raise pH and reduce the amount of dissolved heavy metals from old copper & lead pipe-work), but this doesn't add any dKH buffering.

In a planted tank, if you have water with very low levels of carbonate hardness, the pH is likely to vary over quite a wide range during the normal diurnal cycle. In really soft water this could easily be a swing from pH4 (high CO2 levels before photosynthesis starts) to pH8 (CO2 depleted and the water fully saturated with O2).

This is why people re-mineralise RO (to 4dKH) if they add CO2.

Have a look at <Remineralising RO | UK Aquatic Plant Society>

cheers Darrel


----------

