Same here with Waterworld, had some that have lasted well, others weren't right from day one.
Generally the smaller the fish the more they had problems, don't know if its something to do with higher turnover and getting shunted around too often/quickly.
Also had some problems with their live feed bags upsetting tanks and going cloudy for a few days - I don't know if this happens with other places as well, stopped using live feed, didn't use it often anyway.
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