SynRinse Irrigation Pilot (SIP) Trial

Inclusion Criteria: * age \>= 18 * Meet diagnostic criteria for CRS (as defined by the AAO-HNS 2015 Clinical Practice Guidelines for Adult Sinusitis). * Have undergone at least one functional endoscopic sinus surgery, be at least 6 weeks out from surgery, be free of any complication from surgery, and have patent sinuses confirmed by nasal endoscopy. * Have active sinus disease as defined as purulent sinus discharge visualized on nasal endoscopy. * Have more than mild symptoms as determined by the SNOT-22 with a score \>20. * Be willing to hold off on standard therapy for chronic sinusitis for 1 week including oral antibiotics and/or oral steroids. * If on topical steroids for greater than 1 month (sprays, drops, or irrigation) these will be continued based on the patients' current use (continued if they are already on them, not initiated if they are not on them). * Must be able to irrigate with large volume/low pressure nasal lavage throughout the study. Exclusion Criteria :• Have an allergy to shell fish. * Be able to return for follow up evaluation in 1 week (+ up to 5 days if needed) * Have obstructive nasal polyps * Participants who have used topical antibiotics within 4 weeks of treatment or are actively using them and unwilling to stop * Participants who have used systemic steroids within 4 weeks of treatment * Are unable to give informed consent or complete self-administered questionnaires written in English because of cognitive impairment, language barrier, or severe medical conditions. * Have a terminal illness or significant immune dysfunction. * Have severe or emergent complications from CRS or presence of a sinus tumor. * Patients with Cystic Fibrosis will be recruited in a parallel study. * Participants who are unwilling to discontinue other sinus irrigations treatments and steroid lavage if already on them (including baby shampoo, surfactant, colloid silver, manuka honey, iodine, alcohol, tea tree oil, or any other compound).