you really need to research each fish in your tank and their tolerance for salt, plecos can be sensitive to it, although i have had no problems with low doses, i have read reports of their skin being burned--as a general rule, scaleless fish and tetras usually do not tolerate salt as well as many others....are you having a problem in your tank that you think salt would help? if you aren't having any problems and your fish don't need the salt, I wouldn't add it--you will have better results with treating things such as ich if you start with no salt in your water--the sudden change is more detrimental for the little ichlets.... you don't need aquarium salt, you can use any type of plain salt, not iodized, but something like kosher...if you do decide to add salt, dissolve it before you add it, and be sure not to pour it directly over your plecos, or any of your fish for that matter...salt does help sickened fish or injured fish ( that can tolerate it

) by aiding their slime coat formation and aiding healing--overall if you don't have any livebearers or similar fish that thrive with salt, no ich or illness, no injuries , i wouldn't recommend it at this time....the plecos certainly don't need it