all ulcers are apparently caused by bacteria. not all bacteria causing ulcers are
aeromonas.
before the ulcers there were parasites damaging the slime coat so the bacteria get in
under the slime coat, OR, mechanical damage from spawning. good to keep spawning
mats in the pond, good to have some salt in the pond to stimulate slime coat, and in
spring when water temps get over 55oF all my koi get antibiotic food for the first
couple of weeks as parasites and bacteria wake up. It takes 10 days of above 55oF
water before the immune system of koi comes online. Ingrid