1.) If you pull the pond volume down by 90% and treat with rotenone at the prescribed concentration, then when the pond is full - the remaining chemical is at a minimum of 9 times more diluted than the effective dose.
Yes - It should then be safe if your initial treatment was performed at the correct concentration of usually 1 to 2 ppm all depending on pond conditions and specie of fish to be killed. Diluting the standard rotenone by 3X-9X of the final pond volume treatment concentration after the fish kill, lowers the final application concentration. Even a 3X dilution is evidently enough to allow the usual restocking fish species to survive as noted by the experience by JasonD. This assumes the rotenone kill concentration was 2ppm or lower. Jason did not provide the kill concentration of rotenone that was applied to kill fish.
Question was : If your stocking plan is time dependent (aren't they all?), is there an inexpensive "indicator" fish we can use to test for safe water conditions?
IMO common indicator fish can be bluegill, sub-adult bass, crappie. fathead minnow, pet shop guppies or goldfish.
Statement - I know we sped up the natural process of filling the pond but this tells me Rotenone is not lethal for very long.
Not always a true statement. The rotenone noted by JasonD was later diluted to a non lethal concentration, however this does not mean the rotenone kill concentration is not lethal for longer periods in the original treated pond volume. At least Four (4) main things cause rotenone to lose it's potency: 1.dilution, 2. sunlight exposure , 3. temperature and 4. amount or density and type of suspended particulates in the water column. Rotenone kill concentration decomposes faster the warmer the water and in more sunny conditions. Rotenone applied during cool or cold water and lengthy cloudy days can have kill effectiveness for numerous weeks or a couple of months. Some water conditions and certain species of fish require a higher concentration of rotenone. It all depends. This is why one should have good experience and knowledge when using rotenone which is partly why a pesticide license is required for its purchase.
