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What should be the PAR range for plants in non-CO2 tanks?

Discussion in 'Non-CO2 Methods' started by Marcel G, Nov 14, 2012.

  1. Marcel G

    Marcel G Banned

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    Please, does anyone know what should be the approximate light intensity (µmol PAR) at the substrate for plants in non-CO2 tanks? I was trying to find this answer elsewhere in this forum, but I was not lucky. I recall dutchy's reply in some thread, where he said something about 30-35 µmol PAR. I also want to note that I have measured some tanks where there was 20-30 µmol PAR at the substrate, and some plants were not doing very well + had algae problems (but that could be from another reason also ... but I think that there is also some threshold under which the PAR should not fall for plants to grow well). I also recall one of Tom Barr's newletter concerning light, where there was a graph/table stating LCP (= light compensation point) of some plants: 15 µmol PAR for Hydrilla, 35 µmol PAR for Ceratophyllum and Myriophyllum, and 55 µmol PAR for Cabomba ... so if I understand it right, it means that I need at least this amount of light for the plants to begin grow ... if I add less light, they could stagnate or even die. Is this correct?

    PS: Does anyone know (or can suggest) the LCP for some common aquatic plants we use in non-CO2 tanks?
     
    #1 Marcel G, Nov 14, 2012
    Last edited by a moderator: Nov 14, 2012
  2. jerrybforl

    jerrybforl Lifetime Members
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    I think there is a fine relationship between plants and a PAR that works. You have to choose plants that grow slow and will do well in the lower light. If you're looking at a "low light" non CO2 tank, I would start at 30umol at the substrate.

    The algae comes from several reasons.

    1. Maybe you have too much light.
    2. Excess ferting.
    3. No CO2

    There is a balance between the three. If one or the other is out of sorts, you will have algae issues. Please post your parameters, so that we can better help you.
     
  3. Tom Barr

    Tom Barr Founder
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    30umol is a good range, maybe up to 40-50umol.

    Most use T8's bulbs etc. I'd use 2 per 30cm front to back depth of tank.
    Then about 15 cm above the water's surface.
     
  4. Marcel G

    Marcel G Banned

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    Thanks for your suggestions!

    @jerrybforl: As I stated the tanks were not mine. Recently I don't have any non-CO2 tank, although I plan to set up one.

    I just wanted to know two things:

    1) If I understand it right, each plant has its LCP (= light compensation point), so if the light doesn't reach above it (in the long term), it will not grow or it will suffer? So for example if Cabomba has its LCP = 55 µmol PAR, it means that at light of (say) 30 µmol PAR, it will not do very well ... right? This would confirm my findings in some tanks, where I measured light ... and the intensity was very low (say 20-30 µmol PAR) ... and some plants were not doing well (especially at the substrate level) ... given that other parameters "seemed" to be OK (CO2, water circulation, flow, water quality, ferts ...).
    2) If someone did some experimenting to find out some (rough) LCP's for commonly used plants at non-CO2 tanks?
     
  5. Tom Barr

    Tom Barr Founder
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    LCP changes with CO2............you cannot discuss one......without the other.
    Since plants have differential ability to sequester CO2.............

    CO2 changes a fair amount in planted tanks both locally and for the entire tank.

    Non CO2 tanks even more so.

    You might look at Diana Walstad's article in TAG about CO2 levels in non CO2 planted tanks (you can order TAG from AGA's web site).

    If you do a siesta, the CO2 climbs back up, since plants only use CO2 during the light period.
    I suppose we could see if you did 2 hours on, two hour off........would this grow plants under non cO2 much faster, better than a standard 10 hour photoperiod.

    Say 10 hours, vs 2 hours x 5 with 2 hour lulls in between.
     
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