interesting topic.. I had a monster load of FA last summer (my first full summer) and expected things to be the same this year but I made a few discoveries late last summer that make me believe the same as you in that we're missing a part of the puzzle and here's why... Last year I tried a small batch of water hyacinths that quickly spread in number but after 60 days or so I noticed the plants didn't look all that special/healthy considering all of the FA I had. Not very long after noticing the plants had some yellowish color I had the flood. Within a week those yellowish plants were exploding with bright green colors again and multiplying like toads, but the FA never really came back even though we had many days in the 90's yet last year.
This year, besides building my berms and building a channel around the pond, I think I may have cleaned myself out of nutrients inadvertently y watering all of my grass on the new berms with pond water. I've cycled near 1 million gallons onto the new growth and of course it's been replaced with constant well water with basically nothing in it. My water has color but I may have overdone it by exchanging it like I have. As temps of water get into the 70's it will be interesting to see what happens.

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