Pickerel problems

I can't get pickerel weed to grow. I thought it was sturdy stuff. It
languished last year. I got a few stalks and a bloom but it wasn't
growing fast or well. I think I had it too deep, submerged about 8".
this year I moved it to about 5", and finally to where the water is at
its roots. It's put out little shoots but the first batch rotted and
the current shoots are about 4" tall and have stopped growing.

It's in a pot of Schultz Aquatic Soil. The pot has holes in the bottom
so I put some weed cloth in it to hold the soil in. It's fertilized
with a water lily tablet. All my other plants are growing fine (gotta
thin that darned anacharis). What am I doing wrong?

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