First I would have the water tested. I think there is a strong possibility  
of nitride/nitrate buildup in the water.   Complete water  change out may be 
necessary and dredging much of the sediment out  too.  There are test kits 
available at you local tropical fish store.
 
I don't know much about keeping trout but I used to visit a trout fish  
hatchery in Arkansas and I remember that they stressed the need for fresh  running 
water to keep them in their pools.  
 
Also, you might be able get help from your county agent. 
 
George in Central FL

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