The brown debris you describe sounds exactly like what has shown up in our pool the last couple of weeks. Being a newbie, I obviously have no idea what it is, but fyi I have not added muriatic acid to my pool. Correct me if I am wrong, but it looks like sand from above the water, but it almost dissolves or disintegrates when you touch it?

The vaccum that came with my Intex pool is too low quality to actually catch the fine particles so I have had no way of getting it out of the pool, as of yet. I just "stir it up" and then it simply settles back to the bottom a couple hours after vacuuming. It sounds as if you may vacuum directly to the filter so this isn't a problem for you.

I have another thread on here about this too so hopefully between the two threads somebody will be able to tell us what it is and how to keep it from coming back.