Quickdaddy,
My geothermal system discharges into my 3/4 acre warmwater pond with no problems. I suppose I could get it to splash (true ground water is void in oxygen), but when I consider the small amount of intermittent discharge vs. the pond volume itself (about 1 million gallons) it's inconsequential. If there is any area around the discharge of low D.O. before it gets mixed with the water that is high in D.O. the fish would avoid it anyway.
I really would not worry about it (as far as D.O.) and adding some water to make up for evaporation is a plus with no real negatives.
BTW you're probably talking 10 gpm's max if that at all and it doesn't run constantly although it can get close to that in really hot or cold weather.
