WPG rules?

Discussion in 'Lighting' started by Ark, 11 Jun 2008.

  1. Ark

    Ark Member

    Joined:
    15 Oct 2007
    Messages:
    136
    Location:
    Hanham Bristol
    im sceptical towards the whole wpg rule.

    i have a few q's and could do with some a's.

    1) do you use uk or us gallons
    2) does it apply for t5 or t8 lights

    also ive heard doesnt apply for nanos or big tanks so what size (ltrs) does it apply for ?

    Ark
     
  2. ceg4048

    ceg4048 Expert/Global Moderator Staff Member

    Joined:
    11 Jul 2007
    Messages:
    8,953
    Location:
    Chicago, USA
    Ark,
    The wpg rule is like the dropchecker. It's completely bogus but it's the only thing we have that someone can look at and instantly have an idea whether the lighting is on target or not. At the end of the the day it's either use wpg or study Einstein's Special Relativity for the next 4 years at Cambridge University. Now, which would you prefer? For tank sizes between 20 gallons US to about 100 Gallons US it's a pretty good rule of thumb. These days it's more apt to be relevant to T5's and MH. There is more breathing room with T8.

    So that if you have a 30 gallon tank and you said you had 2 wpg T5 or greater I can tell you without a shadow of a doubt that you should be injecting CO2, especially if those lamps have reflectors. Again, crude but effective. This does not mean that you can't run an un-injected 2wpg 30 gallon tank successfully, only that injection would give you better odds of success.

    Once you get beyond 100G or lower than 20G then it's a matter of feeling your way. You can probably apply the wpg rule at the low end but the available bulb choices are not as plentiful so you wind up using 11 watt or 18 watt bulbs and so forth. At the high end you need to refrain from the wpg rule if for no other reason than that your electricity bill will send you to the poor house.

    This is not to say that you can't apply the rule for large tanks, but if you do there are brutal ramification in big tanks. The filter throughput rule becomes more important, the CO2 injection techniques become more difficult and the dosing rules also start to break down. So lets say you have a 300 USGallon tank. Normally 400-500 watts T5 or MH lighting would be the most you'd want to use - but that's less than 2 wpg and yet it still counts as a high light tank with CO2 injection compulsory. You'd want that 3000 gallon per hour throughput even if most of it were just recirculation because you've got to move that water around. The CO2 consumption becomes tedious and the injection methods become difficult.

    In fact wpg breaks down terribly if filter throughput is poor for any tank because you must deliver nutrients and CO2 to the surface of the leaf with greater efficiency as the amount of light increases. So wpg is sort of an all inclusive rule of thumb that takes into account the volume being illuminated, the nutrient delivery and the CO2 injection. It is not just an arbitrary rule based on wattage alone.

    Not sure if this helps. :rolleyes:

    Cheers,
     
  3. Ark

    Ark Member

    Joined:
    15 Oct 2007
    Messages:
    136
    Location:
    Hanham Bristol
    funnily enough i understand..

    my tank is 32 usg
    and has two 18w t8 bulbs w/reflectors = 1.125 wpg
    i have got pressurized co2, and dose tpn+ every other day
    and i have a tetra tec ex1200 so i have a very large turnover rate

    so is this balanced out enough to grow some low-medium light plants
     
  4. ceg4048

    ceg4048 Expert/Global Moderator Staff Member

    Joined:
    11 Jul 2007
    Messages:
    8,953
    Location:
    Chicago, USA
    Yes, I reckon you are on the lowish side and you could easily add another bulb whether that be T8 or T5. The fact that you've got pressurized CO2 means you'll have a lot more flexibility so if you wanted to try some more difficult plants you could just add a bit more light and increase the injection rate. :D

    Cheers,
     

Share This Page

Facebook Page
Twitter Page
  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice