Has anyone ever found they were running their lights to low to discourage algea growth but instead ended up retarding plant growth and giving the algea a better chance to grow?
I have, but not because I was trying to solve an algae problem. I simply though my lights were adequate when they were in fact marginal.
The interesting thing during this time is that I found reducing
(but not eliminating) phosphorus dosage greatly reduced algae, with almost no effect on the plants. That's at odds with conventional wisdom, and led me down the wrong path for a while. Looking back on it now, the only explanation I've found is that I must have been forcing the plants to consume alternate phosphorus sources, in particular organic wastes that may have a specific role in promoting algae growth.
Of course, increasing lighting both improved plant growth and
eliminated the algae. It seems the plants were then growing fast enough to naturally control organic waste levels, without having to manipulate them into doing so by limitation.
It's also not the first time I've seen phosphorus have unexpected effects on algae. I've created some spectacular multi-algae blooms in the past by adding phosphoric acid
(used as a pH reducer), whereas it's been proven that adding huge amounts of potassium phosphate
doesn't have the same effect.
All this leads me to believe that algae prefers specific forms of nutrients. When all is well, plants out-compete algae for those specific
forms, even though the total
amount of that nutrient present and utilizable by the plants may be effectively unlimited. Too little light and plants can no longer do this.