Used to fish up north in a little lake here in Mo called bean lake, the Missouri conversation raised crappie there, lake was loaded with 6=8" crappie, but out in the lake was one piece of 1" metal pipe sticking up in 4' fow, I could catch one 11" to 12" crappie off of it everytime I went out..... so what you have should work, just a timing thing I think........here you on the concrete setting up, for some reason it takes about 3 days for my buckets cement to set up real good, or coffee can weights I pour take about the same time, may be the plastic??