Who has not replace fan on their Nano tank yet ? I tought I could extend their life by shutting them down at night....NOT ! I found out that many of those Fan are using the cheapest possible fan. The stock fans use sleeve bearings and have a bad tendency to die or become noisier while slowing down after 3 months. The best thing to get is dual bearing fan.
I found what I was looking for at: ca.mouser.com and then just select you Fan size and do a search. For my Biocube I picked at nice set of 60mm X 25mm sure their are ticker but they are a perfect fit, I just replace the original screws by longer ones.....I gain more endurance and more CFM. Price was fair.....even cheaper than the stock fan.....and delivered to my door.
More CFM usually means more noise.
How do they compare in sound to the stock ones?
A little more noisy but not that bad. And the canopy is way cooler