There really isn’t a conclusive way for the home hobbyist to determine whether a problem with weak snick or any of the related feeding disorders is due to ectoparasites that invade the gills, perhaps aggravated by secondary bacterial infections that affect the suctorial feeding mechanism, or not. If the weak snick is accompanied by respiratory distress (e.g., huffing, rapid respirations, labored breathing) that’s a good indication that protozoan parasites could be involved, and if more than one seahorse seems to be affected, that it is often a sensible problem to treat the tank for a potential parasite problem.
There are number of ways this can be accomplished such as administering hyposalinity at a certain level and/or treating the main tank with antiparasitics in conjunction with therapeutic dips, but the appropriate treatment method depends on whether or not there are any sensitive invertebrates in the aquarium that might be harmed by antiparasitic medications or fare poorly at reduced salinity.
If you can give me a rundown of all the specimens in your seahorse tank and the current water quality parameters for the aquarium, I will be happy to help you determine the best treatment option for your case, Toni. Please get back to me with a list of all of the fish and invertebrates in your seahorse tank and we can go from there.