Alka seltzer plus cold day plus night effervescent dissolve quickly in hydrating water and are instantly ready to start working whether need it during the day or at night. This formula has improved, less sodium and is each dose is individually wrapped and transforms in just of water into a liquid fast medicine. Product Benefits. Nasal Congestion. Headache Plus Body Ache. Cough. Sore Throat. Sinus Pressure.