The things that Jeffhasapond previously mentioned plus numerous others should be considered or evaluated when doing aeration correctly.
AT LEAST several factors contributed to your fish kill. Some I my not address.
1. Soaker hose will move lots of water due to it producing very small bubbles; usually smaller bubbles than a membrane diffuser, often significantly smaller. Smaller bubbles more water than larger bubbles.
2. Stronger more powerful boil. Diffuser at 25 ft deep will create a very strong boil due to the further distance the bubbles have to travel to the surface compared to 10 or 15 ft.
3. With soaker hose laid directly on bottom, it re-suspended a fair amount of sedimented organics in the first period of operation. Suspended organics will contribute to and increase amount of biological oxygen demand above what pond normally experiences.
4. Summer water temps (80-90F) cause water to hold one half as much dissolved oxygen at 100% saturation as cool or cold water (39F).
5. ALL Water deeper than 6-8 ft in the pond at this time of yr probably had no DO. The DO that was there had been replaced by hydrogen sulfide (H2S) a highly poisonous gas to fish.
6. The volume of water in the deep unmixed zone of a deep pond is significant compared to that of a shallower pond of 10-14ft.
7. Moving a high volume of deoxygenated, poison laden hydrogen sulfide water the contained resuspended H2S sediments that increased oxygen demand in hot weather with maybe little sunny weather caused a large DO sag just before dark. In darkness the entire situation deterioriated and DO was dangerously low at daylight - morning - fish pipping.
8. Large amounts of Moss around edges enhanced the loss of DO at night since it uses oxygen at night vs producing DO during daylight.
9. Additional running of aerator the second day brought even more "bad" conditions and sediment laden water to the surface for twice as long as the first day. IMO that was enough to further degrade the upper water to DO below 4ppm to concentrations of 3 or less - levels that can kill fish esp when the H2S poison is also present. Strength or concentration of H2S in the unmixed zone plays a big role in this scenario
9. Diffusers on the bottom should ALWAYS be separated from the bottom sediments with either distance (on a stand) or a shield or bottom separator plate so the upwelling water is not in direct contact with the sediments so rising upwelling bubbles bring them to the surface. This rule is esp important during start-up aeration during early or mid-summer when increased H2S can make situations worse.
10 Normally one would not get into a fish kill with only running an aerator for 15 min the 1st day but certain conditions as noted above can COMBINE to make even 15 min of run time very risky and dangerous.
I hope your air compressor was not a rotary vane model. They are designed to only operate at a maximum of 18 ft deep. Operation at deeper depths shortens the life of the unit. Compressor for depths greater than 18 ft should be piston, rocking piston, or possibly, but not preferred, a diaphragm.
Last edited by Bill Cody; 07/08/08 09:35 PM.
