There's a lot written about it, so by searching you can get a lot of suggestions of things to try There are many different possible factors, and it can take some trial and error to find what works for you. Since you say the only difference is the filament, and your bed temp is only 50, then that would be my first guess. Try raising to 60 and see if it improves. I think it shouldn't be necessary to go higher for PLA.. if it's better, but not totally solved, try raising carefully some more by small amounts and observe what happens.