Light and pH - The Planted Tank Forum
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post #1 of 3 (permalink) Old 12-23-2003, 07:47 PM Thread Starter
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Location: Cape Town
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Hi once again on my quest to the holy grail of understanding all things planted (in water).

I sat and pondered the light issue, you may know by now I have softish water, which I am in the process of buffering.
At first I noticed a heavy drop in pH and allthough this did go up (very much) the first night it went even lower the next day.

So i started penciling a kind of graph (i know these processes arent quite as linear) which roughly indicates the relationship between the hours of lighting and pH level.

How was I contributing to the increased swings daily?

well, by extending lighing hours, I will attach my little graph at the end...

Extra light will increase the period during which the pH will rise forming more basic (alcaline)conditions, I suppose its slightly cumulative to the point/threshold where buffers will restrain it. I.e. on day 2 the pH could go even higher...

The shorter light day had a smaller rise in pH and during the longer dark period the pH had longer time to drop, and over time would appear to apeal to water going more acidic (until buffer kicks in)??

Even day night alows for equal times for pH increase and decrease = more stable conditions which with the addition of buffer would create smaller swings. I do still think there might be a slight(or nasty) swing if CO2 levels varied alot/stopped for some reason.

Now I doubt that the rate at which the pH climbs and falls in light and dark are equal (like in my picture), but please bear with my train of thought and over simplification unless you can point out specific faults or ways to correct them.

This might at best be confirmation of previously established advice.
At worst you can correct some missconceptions about the processes and scales involved in the light cycle.

Lets talk...

Cape Town, South Africa.

Hi. I'm back.
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post #2 of 3 (permalink) Old 12-24-2003, 02:05 AM
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Join Date: Jul 2002
Location: Naugatuck, CT.
Posts: 2,647
The reason your tank experiences these ph swings is because of the plants uptake of co2 during the day which raises the ph. At night the plants form co2 which lowers the ph.


75 gal heavily planted,50/50 Black beauty,Eco-complete substrate, Pressurised CO2 with solenoid, ph controller, AB Reactor 1000, 330 watts 9325K GE PC lighting,Ehiem Liquidoser, 2-Filstar xp3 canisters.
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post #3 of 3 (permalink) Old 12-24-2003, 02:34 AM
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Location: Monterey, CA
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If you are able to measure pH very precisely, you could stop CO2 injection at nighttime, and see how the pH is in the morning. This might even out the lows, making the swing less pronounced.

Likewise, adding more CO2 during the daytime will reduce the pH increase.

I doubt, however, that you will be able to measure this exactly with the common liquid pH test. An electronic pH tester, oh... how I want one!
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