Since moving house 8 weeks ago iv'e inherited a fish pond containing around 20 fish which is 270cm in length, 130cm wide, and 35cm deep in the middle. It uses a Hozelock Cyprio Ecopower Plus 5000 Filter which has a maximum flow rate of 2250 LPH.
I have never owned fish before, so reading the instructions on the back of the fish food the previous owners left behind it said to feed them 3 times a day, as much as they can eat in a few minutes. I felt this was a lot, because they only manage one cup in a few minutes and talking to others it would seem to be. So i have been feeding them once a day, usually around 6pm. They have one cup full of this(the cup is in the picture)...
This morning 5 of the fish are dead and i am concerned that there is something wrong with the pond water, pond itself, or the feeding pattern.
At least one of the fish in this picture looks swollen, or is that normal?
I looked in the filter and can see lots of insects that look like black maggots inside moving around (those black things on the foam)....
Could there be a problem with the filter? should there be insects/life inside?
The fish that are alive don't appear to be interested in the food today (you can see it floating on top of the water in the first picture).
Also is the pond too busy? there are quite a lot of lilly pads, and the plant towards the bottom end on the right has grown significantly recently. Could the fish be getting trapped or stuck in one area of the pond?
Behaviour wise, they seem to congregate by the water inlet, gulping at it. And often come to the surface and just gulp, ignoring the food. One of them is constantly swimming on its side in a shallow area, which is unusual.
Any advice greatly appreciated, as i am concerned that more will die if there is a problem with environment they are living in.
To summarize the key concerns...
Do one or more of the dead fish look swollen? What kind of fish are they? Should the filter have life/insects in it? and is it dirty looking? Is the pond overstocked? Should they be gulping at the surface? Is the feeding pattern ok?