Re: Disaster, lost all 13 koi last year and colony of frogs!
#6
Hello and welcome to the site :)
You say the filter has seen little use? The filter will need to be on 24/7 as it's main job is not to keep the water clear but to grow friendly bacteria that consume the ammonia and nitrite in the water. Fish produce ammonia all the time and it's highly toxic to them.
The filter also creates water movement which aids in oxygenating the water far more than a few weeds can and should break up that oily surface film.
It takes 6-8 weeks to build a colony of bacteria in a filter that can help detoxify the water. So turning the filter on now isn't going to be enough to save the day. Can you test the water for ammonia, I think this should be your first step. If you find there is ammonia in the water products like AmQuel(used sparingly) and partial water changes will be required until the filter catches up.
A pond expert will be along soon and I'm sure they'll be able to offer more detailed advice - I assume the fiberglass was professionally cured/sealed to make it safe for the fish?