I have a 24' ag pool that has been perfect until last week. I have been using the BBB method since installing the pool in July. However, late last week, we finally had some substantial rain (the first since May). Now, my pool has these brown deposits on the bottom. It tends to cluster in the little foot print divots and along the cove. It almost look like tannins from decayed leaves. But, I had just vacuumed the pool a couple of days before it started doing this.

I decided to brush it and the deposits easily stir up into a brown cloud that turns the pool a weak tea color. Overnight, the deposits settle down on the bottom again. I decided to shock the pool last night to see if it helps. I plan on vacuuming, but when I was brushing, the pole came apart and now I have to fish it off of the bottom and the water is cold right now. We had a low of 59* last night.

My tests results this morning:
FC: 8.5
CC: 0
CYA: approx. 25 (test doesn't show go lower than 30 but starts to cloud at 30)
TA: 60
Calcium: 130
pH: 7.2
1,500 ppm salt

Solar fish (in case this matters)

I added some more bleach after testing to get the chlorine levels higher and will retest in a couple of hours. I know that 8.5 isn't high enough yet. I want to get it to 12+.

Any ideas what this might be? I was thinking about adding DE to the sand filter and stirring up the brown again to see if it would help filter it out.

The filter is a 22" Hayward sand filter with a 2-speed Pentair 1.5 hp pump. I have been using low speed for the past couple of days.