I am in the same boat (pun kinda intended)…
When we moved house, the bloke there said he was gonna clear out the fish but didn’t get round to it. We said it was fine and would deal with it.
What a ballache! Clearing the weed out, keeping the plants in check, unclogging the filter…..etc.
We managed to get rid of the ‘big’ fish last year and have just got rid of the rest of them. I didn’t wanna just chuck them in the river, so managed to find people who actually wanted them & knew what they were doing….
The pond is on two levels – one sunken and one raised; brickwork surround with lining.
We also had the arrival of some amorous frogs and associated frogspawn but looking at it yesterday, it all seems to have died. We were gonna wait until the frogs had all grown up & flown the nest, but probably not necessary now. So, next step will be to pump out rest of the water; might put some of it over garden (apparently the plants love it) and the rest we’ll put down the drain. Then a case of knock it all down, remove liner, fill with knocked down bricks, stick some sharp sand on (I think) & then lay paving slabs.
It cuts right into the patio & must be 3×1.5m in total size. It’s also right outside the door onto the garden, so will make a big difference.
Once that’s done, there’s a patch of paving slabs down the left hand side of the garden (about 6×10′) I’m gonna lift & lay turf on, so increase the green bits…will probably use these slabs to temporarily cover the pond with, until we can afford to re-do the whole lot properly.
At the rate I’m going on house improvements, I should have it done in time for Summer 2020.