HOWEVER, most of my limited pool knowledge comes directly from this forum, so if someone here disagrees with me, they're probably right. Think about it if your pressure is not abnormal and you lose flow, what else could the problem be but in the pump somehow? Meaning, I do not think that the problem is likely due to your chemistry. I can say that my intex DOES NOT do this at all, and has great flow anytime it is running. Sometimes it would happen out of the box, other times on the second or third year of use, after working perfectly up until then (the very reason I decided to get an extended warranty). Reading people's reviews/complaints and experiences, one VERY COMMON complaint was exactly the behavior you are experiencing. I have even seen it said that there's something wrong with the QC testing at Intex, the problems are so common. I researched the Intex filter/pump quite a bit before purchasing it and I ended up buying an extended warranty on it because from what I read if you get a good one, the Intex is a GREAT pump/filter system but there seem to be quite a few lemons.

I ended up getting the intex 2800GPH, which is basically the same thing as yours (with more GPH, obviously). Hey there- I have a Coleman (Intex) 18' pool that came with a pathetically usless cartridge filter and after reading a bunch on this site, I decided that I needed to get a sand filtration system.

Intex pool pump