Pond not deep enough
I purchased a house that has a small pond in front. It is a preformed pond with a ledge about 9" deep and the bottom being maybe 2'? It's about 7x3' wide. I haven't taken a measuring tape to it but almost positive it's not 3ft deep. There is a box filter with bioballs. I replaced the sponges at pump at time of purchase because after sitting all winter and finding dead moles, etc, it was decidely anerobic - you could actually smell the thing from the neighbors house. I drained and cleaned a bit, and have a small comet and shubunkin fish in there right now, along with some Moneywort. I had some hornwort in there but it either died or they ate it! I purchased from an estate, so I can't ask the former owner any questions but the little boy next door tells me the former owner only put one fish in there each year in the past, and that fish always died. based on what I got out of the pond when I moved in, she bought a Koi each year, one too large for a pond this size to sustain. Is it possible to keep any fish in this alive overwinter in temps that usually dont go any lower than -5 tops?