This happens to me sometimes too. I seems that if I don't pull for a few days or even miss one time mine goes thin and white very fast. Over Xmas I was traveling and wasn't able to OP as much as I have been so now I am experiencing a lot of fast thinning oil. I normally just swish for 20 minutes anyway or I will go for 10 min, spit and go again for another 10 min. The oil you are using is fine. Try to use organic if possible. I use spectrum's organic sesame oil and love it. I have been doing this for about 2 1/2 months now so I am no expert but I hope this helps.