Garuf said:
Thanks for the post Ceg.
Would this inturn explain ADA's low levels of co2 and ppms in their ferts? We know their lights are low light so this would mean they can afford to be ran pretty lean?
Does this also mean that lower levels of growth can be achieved by limiting co2 AND ferts but maintaining high levels of light? I often look at the tropica stats and theirs loads of light but not much in the way of flow. How are they doing this? I'm guessing they're dosing lean and co2 limited but I don't see how they can and not run into failure. :S
Generally, the combination of limited CO2/nutrients and high light causes problems. Physiologically, the flow diagram is;
Light==>CO2==>Macronutrients==>Micronutrients
This is a simplification because there are feedback loops. But Lighting drives everything downstream. Plants have some ability to protect themselves from too much light. They produce pigments that reflect harmful wavelengths such as UV or excessive PAR within the visible spectrum.
The idea that those tanks are using the combination of high light and low CO2/nutrients is an illusion.
As you indicated Barr's measurement indicates that in those ADA display tanks the light energy reaching the plants were actually quite low. There are a couple of factors. Just like those energy saving bulbs we buy at Tesco the spectrum of the bulbs have a high green content. Since the human visual cortex responds most strongly to green, the light appears to be bright to our eyes but are lower in PAR output. If there is sufficient green content in the bulb being supplied, one can have a low light tank while giving the illusion that it is a highly lit tank. The object lesson here is that when shopping for light - get a lower wattage ballast with high green content so that the tank will
look brighter to you but will have a less impact on growth demand and will cause less algae due to lower PAR.
The impact and significance of PAR is the reason the WPG rule can only ever be a rule of thumb. We cannot tell precisely what PAR will be delivered as a result of the wattage (or the even more illusionary Lumens), so some people report that a certain tank size with a certain WPG did not cause algae while someone else uses the same WPG on a similar tank and has problems. The PAR, flow or CO2 might be different even though the WPG was the same.
With suspended lighting, all one has to do is to raise the light assembly high enough that the PAR
entering the tank is reduced. Doubling the distance that the light is from the tank cuts the PAR to a quarter of its original value so even if the bulbs are high PAR the energy entering the tank can be managed in this way.
Once you reduce the spectral energy you have a lot more breathing room, and the plants have a lot more tolerance --- even for limiting conditions because they have an ability to make the physiological adjustments to become more efficient CO2 feeders if the tank is CO2 or flow limited, or more efficient nutrient gatherers if the tank is nutrient limited. When the lighting is beyond their threshold for adjustment then they start to cannibalize their own tissues just to survive.
Cheers,