Hello Matt. Adding chemicals other than water treatment to the tank is a bad idea. You don't know for certain if you have a fish problem or not. Just make sure your water chemistry is a good as it should be. Large and regular water changes will always keep your fish tank healthy. Testing the water is fine, but if you're in the habit of changing most of the water every few days, there's no point in testing. You know the chemistry is always right for the fish.Could this be worms?
I noticed some stringy poop I think
I have some Esha Ndx if I need to use it