Hi, just to get it straight in my head... is this a new pond or just a new filter? With fish? It's just been set up for a few weeks? You are just cycling the pond at the -moment? Sorry for so many questions If you could put some info on your profile it would be handy for reference
I done another water change today and it is now acceptable. I dread to think what the reading was at first.
For info: The pond is 1200 litres, with fish and I'm now using a Blagdon Minipond 6000 filter with a Hozelock 2000 pump.
I was originally using one of the in pond all-in-one filters but it wasn't really up to the job. Constant cleaning. If I was upgrading an external filter, I would have swapped the bio media over, but obviously didn't have that option.
I think you're doing the right thing. Monitor the water quality carefully, and do a partial water change if anything gets too high. Aim to reduce the high reading to maybe half of what you consider acceptable. You want to keep the reading somewhat high to feed the bacteria, but not so high that it poisons your fish.
I've never used it, but some zeolite might help you keep the water quality up while your bacteria are catching up with the load.
In hindsight, it might have been a good idea to cycle the new media with ammonia before installing the filter. If you happen to own a time machine, go back and do that. Otherwise, just keep checking the water until the new filter kicks in.