Hi there, when my dad passed away 4 years ago, he entrusted me with looking after his pond and his beloved fish. Over 4 years, I only lost 2 goldfish. I clean the filters 3 times a year, it has a metal grid (big holes) to protect from cats and the heron and the fish have been happy. The pond probably contains about 400 gallons of water-it has a deeper 'barrel' type of section and a more shallow area. (I'm rubbish at dimensions). Over Christmas, we lost 5 fish-all of them have been found dead at the bottom of the pond. I did an emergency filter clean, changed 20% of the water, took the water to a garden centre to be tested (all was within normal levels) and put a pond 'bomb' in there along with some pond weed. All has been going well but then yesterday, found another 4 fish. The pond is at my mum's house but she checks the fish every day. The water is completely clear, all the dead fish are staying at the bottom of the pond which I've found odd as when I've found dead fish in the past, I've found them floating on the top. There are a selection of goldfish and 4 orphs. We now have 11 fish left and I'm at a loss why they are dying suddenly. I'm an emotional wreck because I promised my dad I'd look after them and we've lost 9 in the past month! I live in South Wales, although it's cold at the moment, the pond hasn't frozen at all. Please, any advice about what I can do??? Forgot to say, the fish that have been taken from the pond are in perfect condition, apart from the fact they are dead!