There are many articles online about the benefits of having aquariums in waiting rooms to reduce stress. Below are the the research studies that these articles are based on and back up these findings.

Marine Biota and Psychological Well-Being: A Preliminary Examination of Dose–Response Effects in an Aquarium Setting – Sage Journals

The effects of interacting with fish in aquariums on human health and well-being: A systematic review – National Center for Biotechnology Information

Animal Assisted Therapy and Nutrition in Alzheimer’s Disease – National Center for Biotechnology Information

Here are a few articles:

Fish tanks lower blood pressure and heart rate – The Telegraph

Can Fish And Plants Help Employees Stay More Relaxed? – Healthnetpulse.com

Aquarium Deliver Health and Well Being Benefits – Eurekalert.org