PH of 7.8 is starting to get a little high I think, when did you take that test? PH can go up and down a lot. Lots of times it will spike in the evening. So if your PH was 7.8 in the morning or mid afternoon I wonder if it's spiking into the mid to high 8's in the evening and the fish couldn't handle it? PH high's and low's can be very stressful on fish. Not sure if that was your problem just throwing around ideas?? Like Mr. Eric said you should get a real water test done. Maybe a soil test too if you can.
