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I collected some Vallisneria americana var. americana out of a lake in northern Michigan that was quite red. The lake was surrounded by farms and probably received a lot of runoff, judging from the algal growth that was covering almost everything.

You don't lay out any fertilizer dosing parameters in your post. We need to know that, but my preliminary guess is that your nitrates are low.

 

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I've seen similar intensely red plants in a lake in Southern Vermont. Very lovely actually. I brought some back and after a week they established in an aquarium and completely lost the red colour. I assumed that it was possibly to do with the NO3 dosing I was doing. I did not test the lakewater, but the runoff was limited, algae was not present to any degreee, it was not a eutrophic system and it was very well established with Eurasian milfoil, aponogeton sp. etc.

Andrew Cribb

Aponogeton in a Vermont lake? That's very interesting.

Soveroo,

If your plants are growing very well I can't think of anything. NO3 limitation is the usual culprit for red color in normally green plants.