So in my Pre TFP days I used to let the pool go in the winter. The water temp would drop into the high 40's for the Dec-Feb months.. and I figured hey, its too cold to swim in and algae isn't going grow when its that cold anyway. I even turned off the pumps figuring I could save on the e- bill. During the winter the water always looked clear. Well, I was wrong, without exception I always missed the timing of prepping the pool for the swim season.. first I did it in May, nope its green. Then I tried April, nope turned green on me then too.. So I found I need to start paying attention to my pool in early March, any later and I will have a green mess. All this could have been avoided had I applied the concepts I learned as a Marine grad student to my pool... There is ALWAYS algae in the water, and it can grow at any temp! The amount varies, and the rate of growth varies, depending on the conditions but its always there. You said you get a lot of organics from the trees around you.. so do I, and that is the primary source of the nutrients that I have to deal with.
Fast forward to now, I had since added an SWG, but even with that the Dec-Feb months are still the same protocol since it is too cold to produce chlorine. But its not cold enough that I need to "close" the pool. its more of a soft close. And this is what I find I need to do during that time.
1) Get the organic material that drops into the pool out as soon as possible, the longer its in there the more nutrients will leach into the water.
2) I can reduce my pump run time, but I can't turn it off. The circulation is filtering particulates nutrients. Same with the pool sweep.
3) Maintain some kind of chlorine level. Yeah the conditions are on your side to help suppress the algae growth. but by monitoring the FC I can see when the pool starts to "wake up". I find it to be a combination of the sun getting higher in the sky and the temp of the pool starting to go up. During the winter I only test once a week or every other week since there is not a lot going on in the pool. It hardly takes any time, but this was a huge help to see when the FC demand starts to go up as the season changes. If I had been doing some basic winter testing back in early days I would have seen when the pool was waking up and could have responded accordingly, instead of play Algae roulette. If you are going through that much chlorine in the winter.. there is something going on in your pool.
4) I let my residual CYA level from the summer ride out during the winter. It has less of an effect when the sun is not as high in the sky... and with the trees around my pool it hardly gets any direct sun anyway, but there is some in there. The rainy season here is pretty predicable, For the most part its usually done by March and any rain we get after that I typically won't have to drain the pool to accommodate. That is when I start adding CYA because I know I won't be draining off any water, and coincidentally it corresponds with the sun getting higher in the sky. I start by bringing the CYA up to manual dosing levels on the
FC/CYA Levels and by April I am up to the SWG dosing levels as the SWG is able to handle the FC load.
5) With all the organics I get in the water from garden runoff (the backdrop of my pool is a raised garden area) and tree snot, I find a phosphate treatment helps with that. This is a point that is up for much debate here, since technically if there is no algae then there should be nothing to eat the phosphates. but I find it helps limiting at least that nutrient chemical, so I use it as a part of my opening procedure and then I am done with it. Also there is some anecdotal evidence it makes SWG's run better. The jury is still out on that. Those discussions are scattered around the forum.
Well this turned into a longer post than I thought but the take aways are don't assume there is nothing going on in your pool when its winter, there is. Testing is important even to confirm nothing has changed. Just saying, "hey its clear" and going about your day I find will come back to bite me in the butt.