Here is a spray solution that is designed to last and be effective for about 8 weeks as long as you keep it covered, out of UV light, and keep it in a cool area.
In a glass put 10 ml of 5% sodium chlorite and add 10 ml of 10% citric acid . Let this activate for 10 minutes, then put in into a spray bottle and add enough water to bring the total up to 500 ml.