One of the risks of growing in a cold climate during the winter is that low temperatures can cause salts to crystallize and fall out of solution. The 2 factors to keep in mind are the temperature and the concentration of the fertilizer. The colder the temperature, the less salt the water can hold. A strong fertilizer such as Holland Secret Micro contains a lot of salts and so low temperature fallout is much more likely than for an additive such as Carbo Blast which contains minimal salts.
How to know if fallout has occurred is to gently shake the bottle and if there's a rattling sound resembling broken glass you'll know that the salts have precipitated out of solution. This doesn't mean that the fertilizer should be discarded, but rather that these salts will have to be redissolved before the plants can be fed. Place the bottle in warm water and periodically swirl the bottle gently for 10-20 seconds, repeat until no more rattling can be heard. The warmer the water (not hot as it will damage the plastic bottle, ideally a constant 50 degrees Celsius), the more often it is agitated, and the more dilute the fertilizer the more quickly the salts will be redissolved. Ideally once the process is finished the contents of the bottle should be dumped into a clear container to confirm that no crystals can be seen.
Like most things, preventing the problem before it occurs is the best option. Try your best not to let liquid fertilizers fall under 10 degrees Celsius as anything lower will increase the risk of precipitation. The surefire way however, is to use powdered nutrients and additives as they can tolerate nearly any temperature.