Summer usually means increased pond water loss due to evaporation, which of course leads to adding more water to our ponds.
This is best done with an automatic system if you are topping off with chlorinated water. All city water sources are chlorinated.
An automatic water filler continuously adds just the right amount of water to keep the pond full. By doing this on a constant basis, the amount of water added is very small at one time. This greatly reduces the chlorine level, and this tiny amount evaporates off quickly.
In higher summer temperatures, when most evaporation occurs, chlorine will normally dissipate in a day or two in a crystal clear pond, and much quicker in most of our ponds with normal levels of suspended solids. This is another area in which TOO CLEAN is worse than a normal healthy pond. You want to be able to see the bottom of your pond, but filtering to crystal clear levels like a swimming pool is NOT normal.
All of the inhabitants, plants, and especially floating plants with no access to soil, need an enriched water system to survive. Most floating plants depend upon the movement of water past their roots for food. Your Biological filter is also affected by chlorine, and we will cover that in another Pond Tip.
The tiny amount of chlorine added by using an automatic filler can also be consumed by the solids in the pond.
When we drink water with chlorine added, it kills off a few bacteria in our bodies, but has no major effect on us. In the same way, chlorinated water added to a pond in tiny amounts will have negligible effects on the pond occupants.

Using manual methods or topping off the pond with a hose weekly, adds a large amount of chlorine to the pond at one time.
You should always add dechlorinator when topping off the water level of a pond by manual methods. This amount of chlorine can be harmful to your fish. Even if it is not enough chlorine to mean immediate death to the fish, this higher level of chlorine can still burn the delicate membranes and affect the fishes gill function. In very small ponds, this is very important.

You can add solutions to the pond water that will lock up the chlorine in added water. This is best done by running a hose into a large bucket above the pond and adding the solution to this moving water. This gives the solution plenty of time to act on the chlorine and mix thoroughly. You can find numerous chlorine reducing products at pet stores, aquarium or pond suppliers. Most are designed to remove chlorine, chloramines and heavy metals. They also reduce stress and heal damaged tissue by repairing the slime coat on the fishes body when fish are handled, breeding or under stress for any reason. These products are great for water changes and when adding new fish. As with all chemicals, follow the directions on the product container carefully.