Leave the plants for sure and if they are making the water dirty with their soil next time plant them in water garden soil in a water garden pot, you can get it at any water garden store. Get rid of any chlorine… bad news for fish. I suspect another problem might be the water temp. In this heat we are having now and I live in the north east, I run some fresh cold water into my pond 2 or 3 times a day to keep the temp down. I don’t have chlorinated water. I have two pumps running especially in the heat for the extra oxygen but I am not sure what size your water garden is. If the fish are swimming close to the top and gasping you may need another pump. watergarden.com is a very good site to help with many problems.

The smaller the pond the harder it is to upkeep it and the more problems you are likely to have. Keep the plants in it. They are essential to use up the waste that is in the pond. Keep the water moving. This will keep the water fresh. Moving water holds more oxygen and will not go stagnant. You don’t necessarily need a filter but it would help with a smaller pond because you don’t want a lot of waste building up. Never add city/treated water to your pond. It may contain an overbalance of minerals or ‘other’ that can put a hurt on the balance of your pond. Always use rain, distilled or well water. If you can’t then follow the advise here and treat the city water before you add it.

Plants are a good step – the fish and water need them. Do not ever use bottled water. Instead buy a liquid additive to balance the pH in your water. Check Lowe’s or even better, look in your yellow pages for a nursery that supports water gardeners.
The other thing is don’t change the water. Once the water reaches the good pH, changing it throws everything off balance. Koi are messy fish and they will eat your plants.
We use Barley Straw in our pond every few months to control the algae. Also called a Barley Ball.
Keep your pump going 24/7, all year long. Clean it’s filter regularly and insure the water level doesn’t drop too low.
Have fun….

If you have a water garden with a fountain your fish are getting oxygen,your plants also provide oxygen. Once tap water sets for about 24 hrs. the chlorine in it disappears. If you have goldfish in your pond try floating a block of ice in it during this hot weather,they love cold temps.

Try changing the water frequently and if that doesn’t work, use a water purifier.

defiantly get a water conditioner to take the chlorine and metals out of the water, other than that, it depends on how small you mean by small and how big the fish are. you’re probably ok though