Salt when used to treat for ich should be added at a rate of 1 pound per 100 gallons of water each day until the pond reaches .4% salt. If there is no salt in the pond to start with, this will take 4 days to reach .4%. A 1000 gallon pond will require 40 pounds of salt to reach a salt level of .4%. This may sound like a lot of salt but if you add it over a 4 day period it will not bother the fish or the filter. Leave the salt level at .4% for at least 3 weeks. Ich is easily killed with salt when it come out from under the fish’s scale to reproduce, however it’s life cycle is such that it could take up to 3 weeks to come out and be exposed to the salt water. You can purchase 50 pound bags of solar salt at Home Depot for around $5.00 each. Use the cheapest salt you can find because it will have no additives in it which could be harmful to the koi.