...which brings us back to proper ratios. If anything is limiting in plant growth requirements, algae are more likely to grab hold and use whatever is there that isn't being used by the plants due to lack of something else. In that respect, I don't think it can be narrowed down to lack or excess of any one specific thing - be it lights, CO2 or nutrients. It would seem mostly case specific.
Since I feed mainly frozen food, this is probably why I have experienced the phosphate-algae correlation. FWIW, a while back, I started soaking my frozen food in RO water for about an hour before feeding. The health of the fish doesn't seem to be compromised in the least, and the orthophosphate present in all food is very soluble in water. I figure it can't hurt anything other than the algae I haven't had to deal with in a while. I thaw the food, let it soak, and pour it through a brine shrimp net.
I've been able to condition wild Apistos for breeding since doing this, which would lead me to believe that pre-soaking isn't removing essential nutrients to any large degree.