Stocking up is common with normally active horses that are suddenly confined (by their choice or not) to a smaller area. So long as there is no heat in his legs, I wouldn't really worry about it. I am not sure that I would cold hose him with the temps being that low, just long walks with some trotting outside should be sufficient.
Here is some information copied and pasted from another website.
Treatment is usually pretty straightforward: Get the horse out and give him a little mild exercise such as
hand-walking or longeing. "With a younger horse, the swelling should go down pretty fast, usually within 30 to 60 minutes of activity," says Allday. "But with an older horse, the lymphatics don't work quite as well and the amount of edema is greater, so it takes a little more time to reduce the swelling, sometimes hours."
You can hasten the process by hosing the legs with cold water for 20-30 minutes, Allday suggests.
If the swelling doesn't improve or lasts more than a few days, take further action. Allday recommends applying a medicated poultice containing menthol and Epsom salts (magnesium sulfate). "This has a bit of an anti-inflammatory effect," he says, "The menthol increases circulation while the Epsom salts pull the fluids out through the skin (via a physical osmotic effect). It's a very efficient remedy."
He discourages using a mud-based poultice: "Most are extremely contaminated, and if you apply it over a cut or scrape overnight, it could very well cook bacteria in there and exacerbate the problem."
Nor does Allday recommend sweats as an initial treatment. "Sweats can drive heat into a limb that probably already has some heat in there, and increase soreness," he says. "However, after the swelling disappears and the limb is tight for a couple of days, you can do a horse up in a sweat. This will help to further tighten the limb."
If, despite these measures, static congestion persists for several days, your veterinarian might recommend medications such as acepromazine, corticosteroids, or diuretics, Allday says.
Mild exercise alone to bring down the swelling is usually successful for the majority of cases. However, Davis cautions, "true stocking up usually persists throughout the horse's life and may gradually get worse as the horse ages, although it should not affect his performance or quality of life."
Rather than deal with the problem after it occurs, a better approach is to avoid or reduce the risk of stocking up through management changes.
The single best thing you can do is turn the horse out more frequently, as activity improves circulation. "Providing exercise in between the days you ride or work your horse would help a great deal," says Allday. "Even just some turnout so the horse can move around will help."
If you can't increase your horse's activity through the week, placing supportive wraps on your horse's lower limbs while stalled could solve the problem, Davis states. "Regular trailer (shipping) wraps are fine, as long as they have adequate padding underneath. The idea behind this is to provide pressure, which prevents the fluid from pooling in the lower limbs. Horses should only wear these wraps while stalled, and they should definitely have time during the day without the wraps. A good protocol would be on 12 hours, off 12 hours."
Allday says horses prone to stocking up might also do better with fewer carbohydrates, more fat, and more roughage (beet pulp and/or grass hay) in their diets, and less pellets, oats, or alfalfa. This should help keep a horse's weight down, improve his intestinal motility, and provide adequate nutrients with a lower volume of concentrates.
He also suggests applying astringents such as rubbing alcohol, witch hazel, or leg braces after you have ridden to increase local circulation and reduce the odds of stocking up. "Before you put the horse up, give your horse's legs a good rubdown with astringent--something not many people do anymore," says Allday