Yes, this is undoubtedly an algae bloom. The heaters don't cause the algae, but it is the sunlight. You need the heaters for your fish.
It seems as if you haven't been doing weekly water changes. Perform 25% of a water change every week, and once or twice a month at minimum should you be scraping the walls of the tank to get rid of excess algae.
A 10 gallon tank is too little space for a Pleco, but you can get a snail or two to help keep the algae under control.
Make sure you aren't overstocking your tank. What kind of fish do you have? If you have Goldfish, then you should know that each Fancy Goldfish needs a tank of 20 gallons or more with a filtration system made for tanks twice the size. If you have live bearers such as mollies, guppies, platies, and so on, you should only have two in such a small tank. Anymore would be overstocked, even three would be pushing it.
I suggest you do some more research before purchasing anymore fish.