It is all about WATER temperature, and if your pond's water temperature goes below 10 degrees (C) you should feed them wheatgerm based food, and you should stop altogether when the water temperature gets to 6 degrees or below. That is all off the back of different foods I have bought over the last few years, and my fish seem happy with me following that advice.
I have stopped feeding my fish as of last weekend, they just aren't interested any more and didn't eat anything I gave them. My pond water is 7 degrees right now.
I am by no means an expert, so please don't take all this as hard fact!!
The air pump is all about aeration. Its not so much about bubbles in water, but all about agitating the surface of your pond. If your waterfall creates a lot of surface movement over the pond then you might be ok (I don't know how much is enough).
I added a cheap fountain last year to help aeration, and this year I have replaced it with a proper air pump. Its hard to tell if it has helped, but it certainly hasnt harmed the pond and the fish didn't seem at all phased with the hot weather this year. I am not sure whether I need to run it all year round though, once the fish start to slow down and the plants stop growing then I might turn it off.
The plants I have are: Elodia Crispa (it grows fast, an oxygenating plant) Water soldiers (the fish love swimming under them) 2 water lillies (the fish love the pads) And a tall plant that I cant remember its name (it flowers nicely, no idea if its good for the pond) Oh, and lots and lots of string algea. I have to take out handfulls of the stuff every week, its crazy stuff.
One thing about my pond is that it doesnt get a lot of direct sunlight, maybe 2 hours a day. Plenty of light otherwise, just not direct sunlight.
At the same time as cleaning the filter, I pump out anywhere up to 25% of the pond water (my pond is ~800 liters), normally maybe 10%. This is normally every week.
To fill the pond back up I add some Tetrapond Watersafe Pond Water Treatment and then top up with tap water via a hose.
I can't remember getting anything but 0 or next to 0 ammonia and nitrite, especially since the pond was first set up. The nitrates have never got too high. I have always assumed the regular water replacement, and the high number of plants in the pond have always helped.
Yes I do mean pulling the handle up and down a dozen times then flushing it out via the non-pond outlet (cant remember what it is officially called). My filter is 2 years old and I havent touched the insides of the filter at all except to replace the UV bulb.
Sorry, I didn't see any actual readings for water quality. I've just noticed where you mention them, and yes I would recommend you test for nitrite too. My normal Ammonia/nitrite/nitrate readings are 0/0/0 using a kit similar to API Master freshwater Test Kit.
Hi, Just a quick comment on the filter. I have an Oase Filtoclear and I am assuming your Oase is something similar? For the Filtoclear, it does recommend regular cleaning (the manual says regular, a shop-added advice sheet specifically for that filter said weekly). Sorry if that contradicts what you said Jellybean. I clean mine every week and plenty of green sludge comes out every time. With these types of filters, they are very simple to clean and they automatically use the pond water to flush the filters.
As others have said, water quality is a likely suspect. A decent testing kit or the services of a LFS will help there.
If the fish are dying during hot weather then aeration may be the issue. Lots of agitation on the surface from e.g. a fountain, waterfall, airpump is a good thing. If you have too many oxygenating plants then they could cause problems during the hottest nights as they take oxygen OUT of the water during the night.
As Iain_clark has also said, check for any chemicals that might be getting into the pond. e.g. Any water that runs into your pond may contain chemicals from any treatments that have been applied to the lawn/garden. Paints/Sprays for fences can be deadly to fish too.
Very sorry to hear about your troubles, I hope the fish are doing better now.
I am no expert so I don't want to add anything that might confuse you or make things worse, but one simple thing to consider at this time of year is the oxygen levels in your pond.
How does the water return from your filter into the pond? Is it via a waterfall or something similar that agitates the water surface a lot? That kind of setup helps with oxygen levels.
The symptoms that I saw last year for this were my fish gasping at the surface and dashing around in a stop-start kind of fashion. This was during the very hot days and nights last summer. At the time, I added an extra little fountain to help agitate the surface, and that seemed to help.
This year I have added a decent air pump and I haven't seen the issue again, and we have had some belting hot days this summer.
My pond suffers from string algae, and I have tried a number of things to limit its growth, including:
1) An electronic blanket weed controller (a blagdon one). 2) Barley straw 3) Competing plants (mostly elodea crispa). 4) Shade. The pond doesn't get much direct sunlight, maybe 2 hours a day). 5) An aquarium cleaner/scraper (my pond is a raised fibreglass pond, so is is relatively easy to clean the sides).
It was only towards the end of last summer that the string algae got under control and I no longer had to keep cleaning it out. I've had all winter to think about what the magic formula was for the irradication/control of the algae (ponds are almost boring in the winter!), and here are my very amateur thoughts on the five points mentioned above:
1) Electronic controller - meh, who knows: The electronic controller was installed in the spring. It was running for a long time with no obvious effect, so I am not convinced it is doing much.
2) Barley - Good: The instructions say it takes about six weeks to kick in (it needs to start decomposing). I put it in in early summer, and the pond got under control a few months after that.
3) Plants - Good: By mid summer, the lilies were in full leaf, er pad, and the elodea crispa was rampant. There was now plenty of plants competing for the nutrients, which I suspect is the main reason for the good control of the algae.
4) Shade - Unknown: Not a big issue for me I suspect. The shade was the same all year round, and the plants at their peak only covered maybe 2/3 of the surface, so I dont think shade was the tipping point for the algae to get under control.
5) Manual cleaning - Priceless: Before the pond sorted itself out, the algae made the pond look awful without a bit of cleaning every week.
I would hate someone on here to tell me that string algae stops growing towards the end of summer, as that would mean none of my methods had any effect at all!!
This year I already have the barley in place and it's six week period to start having an effect is up next week so I am hoping to notice the difference soon. I have also kept a lot of plants in the pond (it is now a mature pond, rather than being almost new last year). I am already seeing string algae growth, but the plants aren't yet too active and the barley isn't quite ready. Fingers crossed for an easier year this year!
Just to prove that a saucepan can do the trick, here is a picture of the pond after the second big snowfall during the recent cold spell, followed by the subsequent "saucepan to the rescue" hole I managed to melt through the ice.
The snow was over 9 inches deep, and the ice was over 2 inches thick.