For many goldfish owners, summer has arrived and the water in tanks and ponds is heating up. While fish often seem to do well in warmer weather, watch out for signs of oxygen deficiency. Fish that are near the surface frequently - (after ruling out a pH crash, water problems or disease) - may be needing a better supply of dissolved oxygen in their space.
As temperature rises, the ability of water to carry dissolved oxygen decreases. At the same time, as the water heats up, the goldfish's metabolism speeds up and more oxygen is required. This creates the following conundrum: The warmer the water - the less oxygen ; the warmer the water - the more oxygen goldfish need.
The following are some suggested remedies for circulating dissolved oxygen better in your tank(s).
A water change preferably poured creating bubbles will provide instant oxygen, if temporary. Shading the pond or tank from sunlight will help reduce heat and therefore raise oxygen levels. Plants - while beneficial in the daytime - will absorb oxygen at night so planted tank and tub/barrel/pond owners would also do well to consider adding extra aeration. Surface movement is extremely effective in creating gas exchange - this can be done with air-stones/walls/wands, consider adding extra in the hot weather. Smaller bubbles are more easily dissolved and provide slightly more oxygen. If your filter out tube is below the water surface it will not be providing a significant supply of oxygen- a power head can be attached to point the water at the back wall of the tank and create a fountain effect providing effective aeration.
Further measures: In extreme heat, water should be cooled. there are various ways to go about this and everyone has a different favorite but care should be taken not to plunge temperatures too suddenly (2 or 3 degrees change maximum in an hour)and not to add anything to the tank that will freezer burn a fish. One idea is to keep 2 small bottles - I use 500cc size in a 30 gallon tank - of frozen water in the freezer - and alternate them. Put one plastic bottle in to float and leave the other frozen. When the first frozen bottle has defrosted, you can take it out and add the 2nd frozen, putting the first frozen back in to freeze- and so on. You should be very careful to check the lowering temperature constantly.
Other methods of reducing the water temperature by several degrees are to use a fan, to turn off overhead fluorescent light strips and to remove the tank hood if there is one. Clip on aquarium fans or standing electrical fans are quite effective if pointed directly at the surface of the water.
The oxygen demands of goldfish can double in the first hour after feeding. For this reason if there is insufficient oxygen available then fish should be fed sparingly even though they seem hungrier in the warm weather. Of course if oxygen is plenty available then goldfish will be happy to be fed a little more as their metabolism rises in the warm weather, therefore keeping tanks well aerated means we can do this safely.
Finally, a remedy I have read about but not dared try - is to add in a sprayer only - a 3 % USP solution of hydrogen peroxide - one squirt (1.5 milliliters) per gallon of water. Do not spray on fish and spray below the water surface. this method takes about 30 minutes to take effect. Since over spraying is very risky and can burn fish, this is not a method I would recommend, except for the very experienced but it is said to be effective in raising dissolved oxygen levels.
So please take a moment to consider your aeration as the hot weather progresses. Your fish will be much more active and thank you for it with that loveable happy dance!