Our outside pond is about 300 litres and has a bog filter attached to it. During the winter it can get into the negative Celsius here and I was wondering if there are any algae eaters that would survive at temps that low, the goldfish seem to do fine but all the algae eaters like nerite snails and shrimp need the water to be a bit warmer. Are there any algae eaters that would thrive in a pond like this