Boatdrinks wrote:

I've had my 75 gallon freshwater planted tank up and running for over
two years. The plants are flourishing and I only have five small fish
which includes 2 SAEs. A couple of days after I did a water change
last month I noticed a think floating white film on the surface of the
water. I thought I must have accidentally introduced some soap into
the tank. When I tried to push it all together to scoop out it
clumped and sank to the bottom only to rise to the surface again a few
minutes later.

How often do you change water in the tank, and how much do you change?