Without definite information on the aquarium inhabitants health while filter was used I suggest cleaning inside filter and soaking hoses with a half bleach water in a bucket or tote overnight. I agree with replacing the media.
Seafood is ok although foods like smelt contain thiamine which is not healthy for fish long term.
I personally don't feed cooked fish or shrimp to fish.
Also recommend adding vitachem to shrimp or fish.
I've been keeping fish for years early 80's but now consider myself a true fish hobbyist due to learning from another forum and the resources from the internet.
I have a pair of Doryichthys Martensii that has spawned but male has lost 4 of the developing eggs from his pouch.
Did research on a seahorse forum and found out this happens sometimes with inexperienced pairs.