# Why do we need the drop checker to be green by lights on?



## Andy D (31 Jan 2014)

Hi All,

I'm sure there is an easy answer for this that I am not thinking about so apologies in advance. 

Drop checkers are said to be 2 hours behind when it comes to the colour change so I take this to be that what the drop checker shows indicates the pH 2 hours before.

CO2 concentrations should be at 30ppm by lights on with is generally considered to be a lime green colour on the drop checker.

Therefore why do we need the drop checker to be light green once lights are on? To me it makes sense that the colour of the drop checker 2 hours after lights on is key as this reflects the levels 2 hours before.

Is it just to be sure the levels are right when lights are on?


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## parotet (31 Jan 2014)

Once again looks like another Rubisco thread Lol... I guess a lime green when lights on ensures that when Rubisco is activated it will be able to have enough co2 to make its work...


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## John S (31 Jan 2014)

I think it's just to be sure you have maximum Co2 concentration at lights on. This is when plants will absorb the most. Their usage will tail off during the photo period.


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## Ady34 (1 Feb 2014)

Hi.
Drop checkers are just a guide, to be more 'sure' of having 30ppm for lights on its best not to second guess the dc so having lime green representation for lights on removes as many guesstimates as possible. More often than not even when the dc shows a lime green we still won't be providing 30ppm throughout the tank due to other factors.
Cheerio
Ady


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## ceg4048 (1 Feb 2014)

Andy D said:


> To me it makes sense that the colour of the drop checker 2 hours after lights on is key as this reflects the levels 2 hours before.


Yes, that's entirely logical, but as Ady mentions, it's just a guide. Not all DC's have exactly 2 hours. Some may be 93 minutes, others, 184 minutes. The value "2hr" is another rule of thumb, so checking at that time may just be another illusion.

The only way to have a better clue, outside of spending £1000 for a CO2 meter is to simply do the pH profile check at regular intervals. that will tell you with much greater certainty.

Cheers,


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## Andy D (1 Feb 2014)

Thanks for the replies all. Just wanted to be sure my logic was correct.

I have completed pH profiles and I am happy with that but the drop checker thing was just niggling at me. 

Another niggle mind you is with regards to the pH profile. If CO2 levels are not equal in all areas (hence the need for good flow/distribution) of the tank how can we be sure about the pH profile? Do we need to test different areas of the tank to get a general level? If I stick the pH probe into the tank in say one specific area it could be an area with high or low levels of CO2 and may not represent the tank as a whole. 

Is it just a case that we can never be sure about the levels in all areas (although the plants will tell us) so the pH profile is the best of what we can do without spending the £1000 on a CO2 meter?


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## ceg4048 (1 Feb 2014)

Andy D said:


> I have completed pH profiles and I am happy with that but the drop checker thing was just niggling at me.


Yes, that's why test kits suck. They make you question your own sanity and you have to outsmart them as if you were trying to outsmart your psychoanalyst.

The pH profile at any point in the tank has to be used as a proxy for all the other readings. It does not tell you what the values actually are, only that you have reached the minimum value, and at what time the minimum occurred approximately. Whether you take a reading at the same place every time or whether you take a sample from a random location will not really matter that much. If you want to determine the effect of random locations you can take concurrent samples from two locations and compare the data. Take a sample behind or into the plant bed for example and compare it with readings taken from the surface.




Andy D said:


> it just a case that we can never be sure about the levels in all areas (although the plants will tell us) so the pH profile is the best of what we can do without spending the £1000 on a CO2 meter?


Yes. Sad, but true.
I beg your pardon, I never promised you a rose garden...

Cheers,


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## Andy D (1 Feb 2014)

Thanks!

One day we will all escape The Matrix. One day...


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## Rob P (2 Feb 2014)

Was a question I've almost asked once or twice Andy. My DC is never its lightest colour at lights on, presumably due to time delay, but ph pen readings always tell me I'm at my maximum drop by lights on. Did a good profile check yesterday (new atty put on) and actually tested I'd dropped the full 1.2 drop with almost an hour to go before lights on!!, so adjusted a bit more on my timer to save some gas  Sod the DC colour...


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