Drop checkers - reaction times

GreenNeedle

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19 Jul 2007
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Lincoln UK
I was wondering whether my drop checker (in my avatar) has a longer reaction time than the chameleon style ones.

By this I mean that my drop checker has the thin pipelike par through the centre and therefore has a much smaller surface area for gaseous exchange than the large area of the chameleon.

The reason I ask is because mine takes an age to change colour. maybe 4-5 hours whereas I always read people saying that it should take a couple of hours.

Your thoughts?

AC
 

Ed Seeley

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3 Jul 2007
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Nottingham
As far as I understand it the rate of reaction of your drop checker will be a function of the following:

The size of the air/water interface between the tank's water and the air gap in the drop checker (this is because the larger this area is the more CO2 will be able to come out of solution into the drop checker's air at a time).

The size of the air/solution interface between the air gap in the drop checker and the solution in the drop checker (for the same reasons as above).

The volume of solution in the drop checker (as the larger volume of liquid the more CO2 will need to diffuse into the solution to generate the required pH change).

As a function of the above two, a shallow indicator solution in the drop checker (it's a function of the other two as if the solution will have a small volume and a large surface area it will be shallow and the shallow depth means the whole solution is near to the surface and the CO2 doesn't have to diffuse a long way down).

The temperature (as at higher temperatures diffusion in and out of solution should occur slightly faster).

For all these reason I find my JBL plastic 'Long term pH test' is th fastest reacting drop checker I have. It has a large surface area between tank and drop checker, a large surface area between drop checker gas and solution and a shallow, relatively small amount of solution. That it also has a white background helps when reading it too. Shame it looks less elegant than the glass ones!
 

GreenNeedle

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19 Jul 2007
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So as I see it the comparison between the 'teardrop' that I have and the 'Chameleon' is:

The small tube opening of the 'teardrop' versus the large 'mouth' of the Chameleon makes the 'Teardrop' slower to react.

The air pocket in the Chameleon looks like it maybe more to me.

Allied with my low temperature of 24ºC compared to the 26/27ºC I used to keep has slowed the reaction down.

Therefore if I reduce the 3ml solution I use at the moment to a shallower 2ml then it 'should' speed things up again.

p.s. I bought a 'Chameleon' one for £3.50 inc. shipping last night so in a couple of weeks (from Hong Kong) I can put them side by side and 'test' (Any excuse to test things. lol

The reason for asking was I was wondering if my Ph kit was working at all yesterday. Co2 comes on 2 hours before lights yet 4 hours into the photoperiod all I had was murky blue. However it was bordering on light green at the end of the photoperiod.

Whether this was a reaction to 4/5/6 etc hours previous is obviously unknown so I have no idea what the ppm was at lights on. I am assuming that as the plants would be consuming CO2 during the photoperiod that for it to be green at the end of the photoperiod (2 hours after injection had stopped) would mean that it was at a decent level at the start of the photoperiod.

I was tinkering again just before the photoperiod so this won't have helped. Will watch today and see what happens.

AC
 

GreenNeedle

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19 Jul 2007
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Location
Lincoln UK
Good tip off from Ed there. Reduced the solution from 3ml to 2ml and the end result 2 hours later was this (mid injection period):
DC-1.jpg


Will still be using the 'chameleon' alongside when it arrives.

I will put them side by side with the same ml of solution and equal number of drops so that I can see which reacts quicker. After which I will move them to another area side by side as a double check on the result. If the same reault as the first are then I will then put them in 2 different areas and let you know the results of the 'speed' test.

AC
 

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