Jim wrote:

How about if I run black gas pipe out to the the back end of the pond,
put on a valve there, then something like icemaker tubing into the
pond so that gas bubbles up near the center, then light it.

Does natural gas contain sulfur? If so, I seem to recall something
about Sulfur Dioxide (poison) or Hydrogen Sulfide (rotten egg smell)
being a possible byproduct when mixed with water. I'm sure some of
our chemistry experts will chime in on this one, as I've forgotten
much more about chemistry than I remember.

One can get tanks of any kind of gas one wants. If there is a problem
with contamination, get a tank of pure gas. Anything in the ane family
(methane, butane, propane) will do.

The ever present propane exchange cylinders come to mind. One would
almost certainly have legal liability issues connecting a home made
gizmo to the natural gas supply, which this would avoid.

A lot of hassles would be eliminated, at least at first, with a tank
setup. Don't bother running a permanent gas line, until the cost of the
tanks justifies it, and it doesn't wear out its welcome the first
season.