The larger the tank the less you have to worry about things like the oxygen content of the stored water used or the temperature or bacteria levels. The smaller the water the greater effect the low oxygen level water will have. Your talking about a 14 gallon tank. Unless your only talking about a half gallon or gallon at most being changed at one time I would aereate the awter and warm it slowly for at least a day before its use. Still water is not going to have a very high oxygen content and heating the water quickly will drive off what little oxygen is there. Stored water should preferably be kept with a circulating pump running in it, whether mixed with salt or not, with small containers an airsone should be dropped in for a day. If nothing else consider the water has nothing in it to inhibit bacterial growth as there is no chlorine or chloramine in it, therefore it's bacterial growth has used what ever dissolved oxygen is available to grow or to even survive. Adding this water to your tank without aereating it will mean a lowering of tank dissolved oxygen levels, a probable temporary lowering of the pH and possibly some calcium carbonate precipitation. The sooner you develop good reefing habits the quicker you can sucessfully keep corals and some of the less hardy but typically more beautiful fish.