Hey Faye Rod, WELCOME to FISHLORE!
Did you cycle your tank before adding fish? I am concerned because the ammonia shouldn't be going up if the tank is cycled, and since it is going up and you have fish in, it can be toxic to your fish.
Read the articles at the top of this page on setting up a tank, and the nitrogen cycle. This can save you lots of heartache.
If your ammonia is going up do 25-50% water changes every day till your cycle is finished...you can also add Prime to help de-toxify the ammonia and nitrite....I would also recommend Bio-spira to jump start the cycle.
How big is your tank? What fish do you have in there besides a pleco? Many fish benefit from algae wafers. My mollies need and love them also.....Good Luck