How to i cool down the water in my goldfish tank?

Unless your room temperature rises above 86 degrees or falls below 50 degrees, leave it be. Goldfish live well in room temperature environments without quite well. It is more natural.

"The goldfish is classified as a coldwater fish, and can live in unheated aquaria at a temperature comfortable for humans. However, rapid changes in temperature (for example in an office building in winter when the heat is turned off at night) can kill them, especially if the tank is small. Care must also be taken when adding water, as the new water may be of a different temperature. Temperatures under about 10 °C (50 °F) are dangerous to fancy varieties, though commons and comets can survive slightly lower temperatures. Extremely high temperatures (over 30 °C (86 °F) can also harm goldfish. However, higher temperatures may help fight protozoan infestations by accelerating the parasite's life-cycle—thus eliminating it more quickly. The optimum temperature for goldfish is between 20 °C (68 °F) and 22 °C (72 °F)." (Wikimedia)

"Water temperature for Betta fish runs from 80 to 82 degrees (°F) " (Setting Up the Ideal Water Temperature for Betta Fish)

Therefore, if your goldfish tank is feels a few degrees cooler, your goldfish are okay.

Cool Goldfish Tank

First try placing a fan so that it blows directly over the surface of the tank's water. If that doesn't work try moving the tank to a cooler part of the room.

If that doesn't work it's time to buy a chiller. OK, this maybe a bit much for a goldfish but I believe all pets are family. You can get one at your local fish store. They are the opposite of a heater. It's safe for the fish and keeps a constant temperature, unlike ice. Chillers have really taken off in popularity recently as other parts of the world are starting to keep American freshwater river fish. I guess what is exotic to someone else maybe normal for you. Honestly if you are going to fork over the money for a chiller it maybe easier to get a bigger tank that's less susceptible to water temp changes. Or go all out and build that dream tank. Regardless of what you do, you are obviously a good fish owner, unlike some of the folks who post here. :)

Check the actual temperature before you start fussing.

Goldfish are fine at low end tropical temps, up to about 25C. They can even survive warmer, but it will start to stress them.

So if the goldfish is in a warm room, the water temp might be 23C, and the betta tank is heated to 25C. Only a couple of degrees warmer, but both are at OK temperatures.

Although goldfish prefer cooler conditions, they also live in ponds during the summer, and are kept in tropical countries, so they can handle some warmth.

Ian

Golfish are really hardy, and you won't be able to tell that much of a difference in water even if it's 10 degrees colder than the heated tank, which means you won't be able to tell it's "cold" enough until the temperature difference is like 15 or 20 degrees which would be bad for your fish. Don't stress! People worrying is what usually kills fish. Goldfish are really REALLY hardy.

Well first get a thermometer to get a accurate temp if its still to high try moving the tank to another spot in the room where its cooler if its under a lamp turn the lamp off if its still to warm add a small fan over the tank and allow it to blow over the water that will drop the temp a few degrees

You don't need to do anything. Goldfish can live in cooler water, but that doesn't mean they have to. They simply can tolerate a wider range of temperature than tropical fish.

Drop a crap load of ice in the take. I mean a lot, dont be shy. You can never have too much ice

No matter what you do, the temperature will always be at room temperature.

No! Dont use ice cubes silly...put him in the fridge.