New Member- ?s about white film on aquarium

[jacques]

Hi,
I just signed up & I have a problem with my indoor aquarium.
We have a beautiful 4500 gallon pond with falls & nice Koi & Chebunkins.
In the fall, we pull out our prize fish & put them in a 250 gallon Pond liner lined aquarium. The rest of the fish survive fine with a pond heater but we don't want to take any chances with the big $ fish. I left about 4 inches of water on the bottom of this aquarium when I moved out the fish last May. I forgot about the water being there. Normally I drain it completely & dry it out with towels.
Now there is this milky white deposit on the walls where water was present. Our pond & aquarium water quality paramaters have always been excellent. I can scrub most of this deposit off the walls, but not all. Any ideas or suggestions?
Thanks,
Jacques