Set up 2 new ponds linked by a waterfall bout 3 months ago. Stocked bottom pond with 4 goldfish, 2 koi and 4 comets. All was well with them up till now when over the last couple of days they have stopped feeding and hanging about at the bottom. (not their usual behaviour as its normally a feeding frenzy and they were also very active) . Now one died yest and another 2day. Tested the water and it it looks ok. Whats going on!!! Ima newby at this so any pointers would be greatly appreciated. Thanx