Algal growth limiting factor

What does the number output in the snapshot file represent? I understand the letters (L=light, P=phosphorous, etc.) but if the number is closer to one as opposed to closer to zero what does that indicate? I am also having trouble with the actual output written to the snapshot file. Output to the snapshot file is updated every month of the simulation. The limiting factor for the one algal group modeled outputs zeros and light limited every other output date, even when algae is clearly growing in the simulation. The other output dates have numbers and limiting factors such as phosphorous. Why would this output only give me data on every other output?