As long as it is actually kept in operation the pump and the disturbance level look sufficient for the design of the pond, but yeah, a mention of just how many fish are in there would be handy, looks ok, but it pays to be sure.

The pond is 1.2 meters square and a foot and half deep. I have 4 small orfe, 5 small rudd, 4 small goldfish and 3 small carp. Ive just recently added the rocks and plants. When I first bought the house the guy who kept the pond had 5 big orfe, 3-4 goldfish and 4 big carp and they all looked healthy.

I havnt got long to give you much of an explination but... If your getting very quick blanketweed growth then the nitrate level must be quite high but as youve added other plants this may eventualy fall with the filter going full time and regular water changes. The pond is a little overstocked as the carp will need at least twice the space of that pond to grow without stunting. The Rudd will be fine with this stocking density but the gold fish and carp may find this a problem. LHG is totaly correct from what i can see from the pics. It is highly likely this came in on the plants, how were they displayed at the stockists?
I hope you havnt lost any more of your little freinds!
Ill keep my fingers crossed for you!

Yeah that pond works out at what 140-150 gal? thats not gonna be enough for the carp especially, but the other fish too will be in overstock when adult. Its also too shallow for some of those species and the temperature will probably vary radically on warm days with a massive day/night drop. Even with the filter reducing the ammonia and nitrite youd still get massive nitrate reading, youd have to be changing virtually 50% of the water out a week , it would be more like keeping a densely stocked aquarium, theres no way the nitrate level will self regulate, even the one adult carp at full size could overstock it. Its real stocking capacity with minimal maintenance would he half a dozen goldies or less.

Probably time to get a liquid test kit , get the water qaulity known about properly, those perams, if they are what id estimate them to be will be causing gill damage , and making disease susceptibility far more likely. Even if the fish are small enough now that it isnt a major problem, it soon will be. At that size its really a smaller goldfish only pond.