This can't be right

Hi all, I can't keep my pool clean. It's a brand new AG 25x15 pool with a sand filter. The water is crystal clear EXCEPT for this brown/black sediment that collects in "dead spots" on the bottom of the pool(it looks like dirty lines). When you brush this stuff it disappears in the water. It always comes back fast too. If I vac the pool . It will look like I did nothing in about 4 hrs. I have vac'ed the pool directly out to waste twice and it still comes back. I have tried raising the chlorine levels and lowering the levels. The same with the PH. On a recent trip to the supply store. I had them test my water sample and everything was OK. The only thing they thought it was, is black algae. They sold me black algae killer and that didn't work. The pool came with a cartridge filter system . We even changed to a sand filter to solve this.
WHAT IS IT? I am open to any suggestions. Including selling the pool:D

Not just dust/dirt? In my AG, I have a few small wrinkles and the dust/dirt always seems to settle in them. If you brush or vac (especially if you move the vac head too quickly) the dirt will get suspended in the water, but it then settles back down onto the pool floor. Think this could be the problem you are having?

I sure do think its dust. It's the volume of it that has my perplexed. I'll get 15 to 20 of these lines of this stuff 12 to 18 inches and an inch wide within 24hrs.

I read this on the old forums.

Can you get in the pool yet? If you can reach down and feel the "lines of stuff". If it is gritty it is sand or dirt. If it is slimy it is algae.

If it is algea you need to shock the pool. Depending on you Stabalizer level raise the Chlorine to the appropriate shock level. Keep it at that level for several days and the algae should go away.

Can you post your current readings? In particular a Free Chlorine and a Combined Chlorine Level and a Stabalizer Level. PH and Alkalinity would also be helpful.

like watermom says , if you vac to fast it will get stirred up and not totally vacuumed . do you have any new subdivisions going up near you , or farm fields nearby?.my pool does this in the spring when the farmers are workin the fields. dust clouds are a risin and that blows a long ways . you dont see it but it happens . also a new subdivision went up last year with a lot of excavating in the spring and the pool had lots of what you describe. i go in with goggles on and dive with the vac hose in hand , its therapy for me, i look forward to it after work on a hot day. kids and wife think im some kind of nut but it works for me.

I have and 18x36 IG Vinyl

I have seen this both last year, and the year before. I usually don't get it until mid season (in Kentucky).

I believe you may be seeing Algae of some type. The 'slime or gritty' test will tell you which one for sure.

If shocking and (very very slow) vacuuming won't work - and it's slimy then you may need some algaecide (60% Poly-Oxy-Ethyl-whatever it is - nothing else will do).

Both years that I have had this problem, it was algae, and I was very careful to vacuum very very slowly over all areas that had it, and then shocked the crap out of the pool (several times the first year I had this problem) and it would just come right back.

With my pool (22,000 gallons or so) it takes a whole quart bottle of the Poly-Oxy Algaecide to treat the pool properly (about $20-23 a quart). The slime is gone for the rest of the year.

I always add one quart of the 60% stuff when I close as well - which really helps over the winter.

That's been my experience - and I think $20 or so on the 60% Poly Oxy may very well solve your problem.