Hi
First post....here is my problem

I purchased a hot tub just over 5 years ago. We use it quite regularily and change water every 3 months at most. Now, I have realized that moss is appearing on the cover, mainly where the zippers are. I tried cleaning it off with some bleach last time thinking it would kill it, but it has reappeared after 3-4 months. I plan on changing the cover because the flap where it joins is cracking now and seems to be water logged. Why would the moss appear and how do I prevent it on my new cover? I noticed the moss the first time about 4-5 months ago.
How long should a cover last? I have the hot tub in a 3 season sunroom. Used all year long.

Thanks!

I would suspect that since your tub is sort of indoors, the cover is not getting enough direct sunlight to kill the moss, which probably blew into the room (spores) and landed on the cover, and liked the moist and shady conditions so decided to stay and grow.

Sounds like you need a new cover anyway. I would suggest once you get the new cover, to clean it more regularly with a diluted bleach solution to prevent new moss from taking root. Make sure you rinse the cover several times, or you may end up bleaching out the color of the vinyl. Or perhaps if you can take the cover outside, you can clean it once a month with a power washer (no bleach) and make sure you get in all the little creases around the zipper.