I think for something to cause diarrhea, it would have to be "ingested".
I'd never have an aquarium...but I know they do have to be kept properly cleaned/maintained. There would/could be materials/products/other fish species you could possibly use to create a balance...have you done the research regarding health issues and aquariums?
Of course, cat dander (dried saliva) from cats causes allergies.
Cat bites can cause infection or other problems if not properly cleaned/treated.
I'm allergic to my cat if she scratches me, touches me with her wet nose or bites me, or I touch my eyes after petting her (all my fault)..but I've never had anything but localised problems. We've had her for 15 years.
*Heather* Status..Asacol (3 twice daily); flaring since Dec 22, tapered every 2nd nite (Jan 3)
~diagnosed January 1989 UC (proctosigmoiditis)
~Bentylol (dicyclomine) 20mg as needed
~Probiotics....(Natural Factors Protec, Primadophilus Reuteri Pearls, Natural Factors Ultimate).... @ bedtime
~various digestive enzymes as needed
~Ranitidine (reflux); Effexor XR 75mg(depression); Pulmicort/Airomir (asthma)
~URSO for PSC (or PBC) 500mg X 2 daily (LFTs back to NORMAL!!)
My doc's logic.. "TREAT (FROM)BOTH ENDS" worth it !!!