Normally, doing jala neti one time in a day is sufficient. But in case of severe congestion or sinusitis, one can perform once in the morning and evening. Frequent irrigation of nostris with warm and saline water is not recommended as the mucous layer that is formed inside the nostrils has important function - thermoregulatory as well as microbes filteration. During neti, this layer is dissolved.
If you have performed sutra neti alongwith jala neti, then it is better to perform once in the morning. You can then do ghritt neti. This means that you can pour 5-6 drops of lukewarm desi ghee (clarified butter) in each nostrils at night before sleeping. But this has to be done in lying position on the bed and remain there for 10-15 minutes after doing ghritt neti.
