Overwintering with slime can cause problems. The 2 most common are (a) conversion of stabilizer into ammonia, creating a nightmare start-up situation and (b) biofilm deposition of calcium nodules (what I've called 'sand algae'). But, if you have no stabilizer in the water, (a) is unlikely, and if your calcium hardness is below 80 ppm (b) is unlikely.

If you DO overwinter with slime, be SURE to open a couple of weeks BEFORE you want to swim. It's easiest to clean slime if you open the pool PARTIALLY, by fully enabling circulation, but leaving the cover mostly in place.

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