03-11-2013, 02:48 PM
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I fail to see any relationship with cloudiness...
In a planted tank you use the plant's response and algae to gage the light. This works for both intensity and duration.
The light must first be of sufficient duration to drive photosynthesis in the specific plant species. Mixing high light with moderate and low light plants in the same aquarium can be tricky, and this is one area where beginning planted tank aquarists frequently run into problems. But the intensity is of prime importance; extending the duration cannot compensate for insufficient intensity.
Once you have the intensity suited to the plants, some fiddling with placement of the plants can aid the afore-mentioned issue of those needing more light than others. Floating plants over the lower light species, etc.
Once the intensity is fixed, then the duration can be worked out. Light must be the limiting factor to plant growth. So all nutrients must be available in adequate levels during the period of light. This will keep algae minimal, because the plants out-compete it. IF the light duration extends beyond the nutrient supply, photosynthesis in plants will slow and may stop altogether. This is what allows algae the advantage, and it will proliferate.
Cloudy water should not have any part in this. It may or may not occur, due to organics, bacteria, etc, but it cannot be used as any sort of guide to light. Or shouldn't.