Small, young plecos are algae eaters, but I'm not sure how much they will actually eat. As they get older, they stop eating algae and you will have to supplement their food with wafers

It was a smaller one, maybe 3 inches. I have a feeling critters are getting in my pond.

3" pleco but how big is your pond?

In just one week, it sounds like you're having the problem already before adding the pleco. Also look into the typical solutions for getting rid of algae.

My pond is maybe 100 gallons. It's really small. I'm planning on adding some Pond Blue. I heard it will cut down on the algae growth. I may have to empty some of the water and fill it back up.