Dirty tank?

i have a 10 gallon tank with 3 mollys in it. i put a sucker fish in it about 3 days ago and it dosen't seem to be cleaning the tank. it just stays on one plant. im not shure of wnat kind it is, the handwriting on the recipt is very messy (but it looks like she wrote Pleiostonees). should i get another to help it clean the tank, or give it more time?