As pond season is approaching again, hopefully, it is time for some reminders about how to put your fish back out into the pond.

Over the winter, pond fish kept indoors often get overfed and get too few water changes. We think we are being kind to the fish by feeding them well, but in reality, they need very little food over the winter, and feeding too much can actually poison their water with the waste products.

On the other topic, we may think we are doing lots of water changes because the water evaporates so quickly in the winter due to the extremely low humidity in our homes. So, we are always adding water to the tank. This is not water “change”, it actually makes the water a lot harder because when we are adding in fresh water, we add both H2O and all the minerals and contaminants in our tap water. But, what has evaporated out of the tank is pure, distilled H2O. So, over time, we get a buildup of those minerals and contaminants and waste products the fish produce.

It is essential that, over the winter, we regularly remove water physically from the tank, and then replace it and the evaporated water. This dilutes the waste and mineral buildup.

In the spring, we fill up out ponds with fresh tap water. This water is basically free of the built up minerals and waste that our indoor tanks have accumulated. This means, even though both tank and pond are full of tap water, the chemical composition of each is going to be vastly different, and even though the pond is fresh and clean, the change between the two can stress the fish out dramatically, resulting in disease or even death.

To reduce this issue, do a large number of small water changes in the weeks prior to putting the fish outside. Try to keep water changes to 10%, no more than 20%. Make sure the water going in is exactly the same temperature as the tank. Doing a 10% water change daily for 2 weeks prior to returning the fish to the pond can bring the tank water back to the same chemical composition as the pond water, greatly reducing the stress on the fish going out.

The actual moving of the fish must be done in a way to reduce the temperature shock on the fish going out. Placing them in an aerated bucket and slowly introducing the pond water a few cups at a time over a half hour period, until the water in the bucket has more than doubled (you can remove water from the bucket to the pond to make room). This should slowly temper the water so that it is the same in the bucket as the pond, and then you can release them into the pond.

On a separate aquatic note, the Ministry of Fisheries has issued an invasive species warning about “Moss Balls”. These have been sold for a while to combat algae in aquariums. Recently, some of these have been found to harbour zebra mussels. If you have any of these Moss Balls, please do not flush them, and make sure you do not put water change water from a tank they may be in down the drain. The must be destroyed using either undiluted vinegar, a bleach solution of one cup bleach per gallon of water, or by boiling for 1 full minute. Full information can be located by googling “Canadian fisheries moss ball”