Sounds like you have a really low bioload if you are only feeding 1 cube per day.Just changed my filter sock. Seven days of use, 100 gallons total volume. Feed one cube per day with eight fish.
In my 180 I have an auto feeder feed 4 times per day and I do my best to have one more feeding and I usually do 4 cubes.
The most plausible reason your socks last this long is the low bioload.
