Yes, plecos are great for betta tanks - but only for a while. Plecos are very shy, so will tend to avoid your betta. They will most likely leave each other alone. Your pleco will attack all the debris and extra food that your betta drops to the bottom of the tank.
The only reason why plecos are questionable betta tankmates is because of the tank size. An inch long pleco that you get at the fish store can grow to seven inches within a year. Common plecos can get up to 2 feet, the length of a 10 gallon tank.
And since most betta owners don't keep their betta in an aquarium more than 10 gallons, common plecos are a no. You will need then a tank big enough to handle their size.
Betta fish, or “Siamese Fighting Fish,” are known as fierce fighters and territorial loners. Males in particular tend to have an aggressive attitude towards other males and other fish.
Despite this reputation, it is possible for male bettas to coexist with other species in a community tank. Check out 9 Excellent Male Betta Fish Tank Mates [Infographic], featured on TropicalFishCareGuides.com.
Tip! Tank mate compatibility is crucial to a successful and healthy home aquarium. Click on the links below for guidelines when selecting fish:
Marine Compatibility
Freshwater & Brackish Compatibility