Here in NJ we've had a heat wave. I've been doing small water changes to cool the pond water . I don't know what the ideal temperature is. Can you help me?

70 - 85 F. degrees is optimum.

Once again, thanks Johnny!!!

Goldfish and koi like it in the low 70's degrees F but can take short periods near 80 degrees F. Between 80 and 90, they will survive short term but will be uncomfortable. If the water gets above 85 degrees F, doing water changes with colder water is the best way to help. You can also float ziploc bags of ice in smaller ponds to cool the pond. Be sure the water is well aerated as the oxygen levels will be lower when it's hot. That tends to cause more problems than the heat itself. If the pond water is above 80 degrees F for a long time, coolwater fish may start to die from low oxygen and the heat. If there's enough shade in the pond and varying temperatures (cooler on the bottom), the pond may not be as warm as one thermometer indicates. My 1800 gallon pond thermometer is reading about 78 degrees F even though the air temperature has been going into the 90's every day. That's because the water is slow to change temperature, and it's cooler at night.

You're welcome, Bflygirl.

I have a floating thermometer, and agree, because it floats, it typically reads higher than the water temp actually is in lower levels.

I strongly recommend floaters, hyacinth, lettuce, etc. for shade. The more coverage the better.

Excellent thread!!
I too was wondering about water temp and thought about zip locs w/ice. We are having a streak of hot weather here (yes, we do see the sun sometimes) into the 100's. My hubby put a piece of cardboard over part of the pond for extra shade. It covers about 3/4 of the pond. I remove it late afternoon when the pond is shaded. It helped quite a bit. I was very suprised how cool the water was :)

Excellent idea, tlc. The thing I'd be worried about with cardboard is keeping it dry. I don't know if there's anything in cardboard that could leach out, adhesives, etc. but that would be my concern.

Underwater shade works too. I use a couple pieces of flat rock, slate type material, I've incorporated into my pond as shelves/ledges/caves. The fish love them, not only for summer shade, but also in winter the fish pack into those areas.

Cardboard may have glue and inks that could get into the pond especially is an unexpected rain came through. A wood board would be more tolerant of rain. Sometimes they sell untreated wood as treated wood could leach chemicals that are harmful. We have some old plywood that's weathered outside that's probably finished its leaching. The thing with covering the pond is you want to be sure there is still good gas exchange especially when it's hot. An elevated tarp or arbor is better at keeping out light but not perhaps suffocating the pond. Also, if a pond is covered for too long to keep out the heat, plants may start to die if they're in the dark. For a day or two, it should be fine.

Good point Johnnyboy and Robyn. I should have clarified that when I "put on" the cardboard that it is elevated maybe 8-12 inches from the pond. My pond is 100 gal with lots of "tall" rocks to lay it on and the cardboard does not cover the whole pond, only about 3/4 of the pond. I put it on when the sun is beating down on the water surface and remove it when the pond is starting to get shade from the nearby trees in the afternoon. I do not do this everyday only when the heat is really going to be up there. I made sure that the cardboard that I used was very stiff with lots of plys. I am home during the day so I keep an eye on it. Shade cloth would be better I agree but in a pinch, if you are smart and careful it should work. It did for me anyway :)

I think you're fine, tlc. I get the picture. Thanks for the explaination; I was looking at my pond wondering how you were doing it. Thinking if I were to do it I'd need a piece bigger than a refrigerator box to cover mine, but 100 gallons is not a lot, and you're very conscientious about how you're using it.

I guess I've been lucky so far. I'm in a fairly new development and have found everything from newspapers, to cardboard, to Tyvex wrap, to plastic that has blown into my pond. One time I found a cardboard box bigger than a large ice chest sunk in my pond.

So far it hasn't caused any problems, but I don't want that to be misleading. I have a fairly good size pond. As an example, given equal amounts of toxins; the ratio of parts per million in 100 gallons would be much higher than the parts per million in 1000 gallons. So yea, as the old saying goes; the smaller the pond the easier it is to upset things, so just be careful.