Water test kit
pH up and down
Baking soda and vinegar
Pond netting and stakes
Optional: sand bags to protect pond against surrounding flooding. Pay attention to where your rain gutters will divert the roof water. Can it flood your pond? Will the neighbors water run into your pond? Rising water from the yard can bring incredibly harmful pesticides and fertilizer into your pond and kill your fish.
Know about the oxygen issues that can happen with water stratification. During storms, your fish will most likely move low in your pond so it is very important to keep aeration going. In heavy rain the water column will flip; bottom water will go up, top water will go down. The density change will push oxygen out of the water. This is known as water stratification and happens because the temperature of the rain water from above is hitting a different temperature of pond water and creating separation in the pond. Without aeration, especially in deeper ponds with too many fish, the fish may suffocate. As soon as you can, get waterfalls and aerators turned back on to start the water mixing again. If you lose power, use a clean 5 gallon bucket to take water out of your pond and pour it back in several times to mix the water yourself by hand. Do this several times a day (taking water from the deeper areas if you can) to keep the water mixing until you get power.
Did you know during heavy rains water treatment facilities add extra chlorine and chloramines to the water? If you need to add municipal or city water to your pond for water changes, make sure you double the amount of dechlorinator after a heavy rain to neutralize the city water.
Generally make the area around your pond safe by
Lowering marginal plants to the bottom of the pond to protect them and provide temporary oxygen to the lower waters. These plants won’t survive down here forever, so be sure to move them back to the marginal depth after the storm.
Trim any branches over the pond
Remove any decorative items that may fall in the pond
Stop feeding fish immediately. Fish can go a week without food. This will stop lower the fish waste produced which can protect water conditions.
Unplug any cords that are not on GFI outlets
If you use algaecides, discontinue use during power outage.
Put protective netting over the pond and stake it down. This will help keep leaf debris and small branches out.
Pond Salt: This is a preventative treatment. Use 1 cup of solar salt (not table salt) per 100 gallons of water. This will bring the salt to about .1ppm, at this level it will help keep parasites from attaching to your Koi, heal wounds, will keep the Koi from taking ammonia in through their gills and will help replenish lost slime coat due to stress
After the storm, immediately remove any large debris in the pond and test your pond water. Pay special attention to the nitrate levels. Runoff can bring fertilizers into your pond which will raise the nitrates quickly. Rain water from above can also bring in nitrates. Unfortunately, there is no easy test for pesticide contamination in your water and your best bet if you suspect contamination from surrounding yards are large water changes. Turn on waterfalls, aerators, and pumps to get the water moving and moving oxygen back in.
You may want to consider a bathtub full of clean pretreated water in case you need an emergency tank to quickly transfer koi into because the pond is too damaged or has too much debris. Have a few aerators to keep oxygen moving in bathtub water, otherwise the fish will use up the oxygen in a small space.
Address and neutralize any water conditions.