New pond owner - do's and dont's please

[Saiditagain]

We recently moved into a house with a pond approx 3.3 metres long and 1.8 wide. It's about 40cm deep. It has a water lily in it, about 25-30 small fish 5cm long, three larger ones about 15cm long and several newts. It also has some snails and various insects at the bottom.

Since moving in with the hotter weather the water level has gone down. Can we refill from the tap? We live in a hard water area.

I've taken some water out and it looks clearish with a slight green tinge. Is this ok?

There seems to be a thin oily covering on the surface of the pond - should I remove it, if so how?

Is a pond like this self sustaining? Ie do we need to refresh the water periodically? Do we need to buy oxygen making plants?

There is some green slimy plant growing under the water on a ornament in the pond - could this be algae and should I remove it? I have bought a barley straw pond and put it in the pond which I think should control.

So many questions! Hope someone can help as we don't want to harm any of the inhabitants esp. the newts.

It sounds nice and healthy to me, apart from the oily sheen. When my pond gets that sheen on it it usually means something's decaying in it, ie unhatched frogspawn or too much leaf litter at the bottom. However your pond sounds big enough to self regulate. If the water's reasonably clear I wouldn't worry too much :)

PS yes, oxygenating plants, the more the merrier :)

Only add rain water to your pond. Tap water can have to much chlorine/other additives in it and could upset the balance of your healthy pond. I frequently have to top up during the summer months, I use collected rain water from the water butt. You can pop a water butt on a garage, shed or greenhouse for ease of use in the garden.
Definitely add some more oxygenating plants, as peerie says; "The more the merrier!" I've got to replace all mine as the harsh winter has finished them off, bizarrely the water lily has survived!

I've found the barley ball excellent for keeping the dreaded algae/blanket weed at bay, so definitely get one of those too