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We used to hang ours over the regular cover. Yes it folded in 2 and froze but when you set it back on the hot water it is thawed in 2 seconds.
USER ERROR is the most common cause of this problem.All hot tubs have air venturri's that allow air to be drawn in to the jet stream mixing with water. When you get out of the tub, BE SURE THEY ARE CLOSED. If you ignore them as many people do, they continue to inject air. The air pressure will then build until it is force out by volume accumulated. It has no place to go other than to be exhausted at the weakest point venting out the corners and seams of the cover. Close the venturri's to shut off the air. Leave them on, AND air cools the water. The warm humid air accumulates to escape and condenses in the cold air causing evaporation while forming icicles.While Tman has a good idea, just what do you do with a floating cover while you are using the hot tub? If you lay it down it will spot freeze to the deck and tear. Best option would be to roll it up and stick it in a 5 gallon bucket like a stove pipe.
A new HS Grandee only runs the jet pumps when you turn them on manually. There is no filter cycle to program.It also came factory equipped with an ozone system which adds some air to the tub 24/7.It this is a problem, I suppose you could unplug the ozone generator from the mother board to shut it off - you do NOT want to leave it powered without air going through it - and then cap the air line to stop the little bubbles coming up from the floor.You will have to increase your chlorine a bit to make up for it, but that should stop the airflow and kill the icicles.HTH