Howes and PowerService White bottle are the most commonly used additives. They can be used as directed year round. I use PowerService White bottle all year round as recommended. I do a "double shot" added to my #1 diesel during the Winter. I reach cloud point/gel point somewhere between -7F and -10F. PowerServce911 (red bottle) does not reduce gell point, nor boost cetane. It removes water.
A Mr. Funnel fuel/water separating filter/funnel really removes any water from the diesel fuel. I never had any problems with water in my #1 or #2 diesel fuel when I used it.
I put Power Service, white bottle, into fuel I add to the tank on our Isuzu diesel generator. For the tractor, I don't bother, but it sometimes gets fueled from the Isuzu's 60 gallon tank.
I've only ever had a problem with fuel one time with the tractor. That was when I bought off road diesel. It formed wax in the tank, which plugged up the outlet line. I was able to fish out the wax globs after siphoning the fuel out of the tank. Could have poured warm kerosene into the tank if I had a way of warming it up safely. That's how we washed the filter cloths in propane dewaxing: with hot kerosene.
Only ever had a fuel filter plugging problem in 32 years of driving Benz diesel cars. That was after running 2 or 3 tankfuls with that synthetic diesel mix (forget right now what it's called, oh, bio diesel). Bio cleans the crude out of dino diesel tanks. Guess where the crud goes.
Only ever had a wax formation problem in 32 years once morning on our 220D at -22 F in the morning in Vermont. Car started after about 20 minutes running the lower rad heater. Went down the road about a mile and quit. Let it sit a minute or so. Restarted. Drove about another mile or so. Same thing. After that, it ran fine. Fuel filter on a Benz is right beside the engine block. After a while the filter casing got warm enough to melt the wax. Never used any fuel amendment in the cars except maybe on rare occasion when I got a wild hair up my butt. Actually put some gasoline into the 220D's tank a couple of times though for winters in Vermont. Mercedes actually told us to do this. Then, someone came out, telling us that this is extremely dangerous, as small amounts of gasoline into the tank can cause very combustible vapor in the tank. Car ran fine. Didn't blow up, luckily. I'm still here.
I buy whatever our fuel dealer, the only one in town who offers off-road fuel, sells whenever my two five-gallon cans are empty. Maybe four or five times a year. I don't add additives, and fill I the tank when it gets down to about a quarter tank. I've never had a problem in 20 years of doing this.
On the other hand, it seldom gets down below zero here, and I doubt I've every tried to start the tractor when it's below 10 degrees.