Each spring I decide to try something different next fall to make the Spring start up easier.

One Spring I left the winter cover on until April; I opened to green algae.

The next year I decided to open earlier while the water was still cold enough to prevent algae. My pool is surrounded by pine trees and I spent more time cleaning pine pollen debris out of the pool than I spend cleaning leaves from the pool in the fall.

Last year I poured borax in the pool to prevent algae and decided to balance the pool with the cover on in the Spring. My initial water tests this year were:

Cl = 0
Ammonia= .5
CYA = 0 Using guess strips
pH = 8+
Water temp = 52 to 55 degrees

I will balance the water with muriatic acid and Cl and worry about CYA, TA, salt, & borates later.

So next winter I will consider using bleach during the winter to prevent the CYA to ammonia process.

What level of Cl do you have to maintain during the winter? During the summer I normally maintain 5 ppm. At water temperature below 60 algae should not be much of an issue. If you maintain 1 to 2 ppm of Cl is that sufficient to prevent bacteria?

You're not circulating the water during winter time? If the water is stagnate you might go the route used by many above ground pool owners --- ramp up the chlorine to high shock levels when the water gets cold, then cover it for the duration. The amount of chlorine depends on the initial CYA level, of course. If you start with a CYA of 50 ppm you'd want at least 20 ppm FC (source: pool-school/chlorine_cya_chart_shock)

If you continue to pump throughout the winter, recommend testing the water occasionally and adding enough chlorine to target 5-10% of CYA -- In other words, the same amount of chlorine as during the swim season. 1 - 2 ppm chlorine is more than enough to kill off bacteria; algae is the main concern. For pool water that isn't being circulated, you could try closing a bit later (so the water is really cold when you add the extra chlorine).

If the pool is covered by an opaque cover, the water is below 50 degrees, and the CYA level isn't astronomical, then you just need FC to be above zero during the winter to insure that the CYA doesn't go away.

Make sure that your water is filtering before you rely on any tests. Even levels in your pool tend to settle when your pool sits stagnant. Youll probably notice a change in levels when you start filtering.