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How much light...

Larry Rogers

Member
5 Year Member
Messages
91
...is too much, without adding CO2?
there is no formulaic answer. You must consider length of day,intensity, and range of lighting. you must also remember that plant density can have an adverse effect on oxygenation at night. At night plants give off CO2 and absorb oxygen just like fish.
 

dw1305

Well-Known Member
5 Year Member
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2,755
Location
Wiltshire UK
Hi all,
At night plants give off CO2 and absorb oxygen just like fish.
They do. They only become net oxygen producers when light levels reach "light compensation point".
you must also remember that plant density can have an adverse effect on oxygenation at night.
This makes sense, but it isn't actually true in practice away from a very limited range of circumstances.

The reasons for this are that in a planted tank:
  • At the end of the photoperiod the water is fully saturated with oxygen, and at, or below, ambient CO2 levels.
  • The internal air spaces within the plants are saturated with oxygen, and a lot of the the oxygen used for respiration by the plant comes from this source.
  • Plant roots aerate the sediment, creating zones where extra microbial oxidation will occur.
  • Plants take up ammonia, and the aerobic microbial oxidation of NH3 > NO2 > NO3 is an oxygen intensive process.
The most common circumstance where plant growth can cause de-oxygenation are where you have a deep tank (small surface area to volume ratio) with very limited water flow. In this scenario high CO2 levels, combined with low levels of dissolved oxygen (via the "Bohr - Root" effects), can cause fish death. Large, bottom dwelling rheophilic fish are especially vulnerable.

In planted tanks fish death, due to low oxygen levels, always happens at night, and often when you have the combination of warm temperatures (gases are less soluble at higher temperatures) and low atmospheric pressure (gases are less soluble at lower pressure). This leads to the, not unnatural, conclusion that the plants are responsible, and at the very end this is true, and they are "the straw that breaks the camel's back".

What it is less obvious is that in a tank, with exactly the same parameters, fish death would have already occurred without plants. Plants increase the carrying capacity of an aquarium.

The work we did with landfill leachates shows that plant/microbe systems are considerably more efficient than "microbe alone" systems for biological filtration.

cheers Darrel
 

abrooks12376

Active Member
Messages
201
Short of the long... yes! Well if you don't like algae farms. Ferts aside.. if their is too much light present and not enough co2 algae will often take over the tank which can kill plants and even fish (oxygen depletion) this would be an extreme case of neglect though.
 

dw1305

Well-Known Member
5 Year Member
Messages
2,755
Location
Wiltshire UK
Hi all,
How much light...is too much, without adding CO2?
As well as having a shorter photo-period, you can add floating plants if you have have very high light intensity.

Because floating, or emergent plants, aren't carbon limited, they will carry on growing in the "high light/low nutrients scenario". I maintain tanks with a lot of light, high plant biomass and low levels of algae without using added CO2 or Estimative Index etc.

Have a look at this thread on UKAPS for some more details <"What exactly causes BBA...">. If you do want to go high tech. I'd join the UKAPS forum.

It was to take CO2 out of the equation that I used a floater for the <"Duckweed Index">.

Very informative. Thank you.
The "plants killed my fish" thread comes up quite frequently on other cichlid and catfish forums, and I understand why people come to this conclusion.

There are a couple of recent threads on "PlanetCatfish" that cover the whole "nitrification/de-nitrification/plants and cycling" area fairly thoroughly. These are <"Cycling question"> and <"Using deep gravel">, and linked threads.

I wrote an article specifically about the processes that effect oxygen levels in the aquarium <"Aeration and dissolved oxygen in the aquarium">, the rationale behind writing it is here: <"Achieving high oxygenation">.

cheers Darrel
 

Karin

Active Member
5 Year Member
Messages
153
Location
Buenos Aires
Hi guys, thanks for answering.

So, I am thinking on upgrading the lights in my low tech Apisto tank. But not very convinced… I think probably not, not sure yet. I already have a planted tank and don’t want to add CO2 to this one…although I could add NPK etc if needed as Duckweed Index will tell! Thanks Darrel! Thanks for the articles. Thanks all.

The tank. I changed the substrate two weeks ago. No apistos yet. The male is doing great in a second tank. There are in there just a few Cnesterodon descemmaculatus and three new hatchets. Java fern, Riccia, Java moss, Echinodorus bleheri, Ceratopteris thalicroides, Anubias. Floaters. Leaf litter (Quercus palustris, Magnolia grandiflora, Platanus hispanica)… Plants do OK anyway but of course not many species. I like aerial growth.

One Sylvania Aquatar 18W (T8, 10000K).
 

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dw1305

Well-Known Member
5 Year Member
Messages
2,755
Location
Wiltshire UK
Hi all,
So, I am thinking on upgrading the lights in my low tech Apisto tank. But not very convinced… I think probably not, not sure yet. ......One Sylvania Aquatar 18W (T8, 10000K).
The tank (below) looks really good as an Apistogramma tank.
dscn6947-jpg.5084


If you want a bit more growth from your submerged plants you could either take away a few of the floaters, or a get a higher intensity light, and let the biomass increase.

Personally I'm a great believer in "if it aint broke don't fix it".

cheers Darrel
 

Karin

Active Member
5 Year Member
Messages
153
Location
Buenos Aires
Thanks again Darrell. I think this could probably be one interesting option and I quote:
Because floating, or emergent plants, aren't carbon limited, they will carry on growing in the "high light/low nutrients scenario". I maintain tanks with a lot of light, high plant biomass and low levels of algae without using added CO2 or Estimative Index etc.

I can add some more light to increase biomass then. Otherwise and according to your belief I´ll just change the bulb as it probably is kind of wore out (i cant even recall when I last change it!:)).
 

dw1305

Well-Known Member
5 Year Member
Messages
2,755
Location
Wiltshire UK
Hi all,
Otherwise and according to your belief I´ll just change the bulb as it probably is kind of wore out (i cant even recall when I last change it!:)).
If it is an electronic ballast (the light doesn't flicker when you turn it on) you only really need to replace the tube when it stops working.

Modern triphosphor fluorescent tubes show relatively little lamp lumen deprecation.
benefits-of-t5-lighting-lumen-maintenance-curves-compared-to-t8-and-t12-lighting.jpg

cheers DArrel
 

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