I'm having a recurring problem with the water in my Endless Pool. Several times over the past two years, the water has developed a brown tint (almost can't see the 42" bottom). Before I discovered TFP, I was following EP's recommendations, which were to keep the FC above 0.5 and to use the Nature2 purifier cartridge, which sits in the skimmer box. Once, an EP tech recommended changing the cartridge filters and "shocking" the water to 5.0 FC and keeping it there until the water cleared. That eventually worked. The next time it tried it, that process didn't work, and I tested for phosphates, which were way over 1000 ppb. (I've heard pool store people say city water is very high in phosphates in my area). I used a copper fungicide and phosphate remover (I don't remember what brand), and the water eventually cleared. After that, I added 3 oz of Pool Perfect + PhosFree weekly (to keep the phosphates in check). The water stayed clear for several months, but the brown returned a month ago. The phosphates again were way over 1000 ppb, so I used the recommended, repeated doses of "commercial strength" PhosFree, but the level wouldn't come down. Algaecide also didn't clear the water.
The pool is indoors (basement), where there is little sunlight and is covered when not in use. I use 8.25% bleach for sanitation.
Here are the test results from last weekend (using a Taylor K-2006 test kit):
Water temp: 84 degrees F.
Pool capacity: 2200 gallons
Last weekend, I decided to slam the pool as recommended here at TFP. Pool Math told me the recommended "slamming" FC level was 17.0. I brought it up to that level and kept it there (testing every 30 minutes, and then hourly after the first night). The FC level dropped quickly at first, but then would remain at around 11-14 after a couple of hours, so I started testing and adjusting the FC four and then three times per day. This morning (about 10 hours after I tested and added bleach the night before), the FC level was 12 and CC was 1.0. The water remains brown, and I'm wondering if I'm on the right track.
Should I continue slamming, or is there something I'm missing? I'm grateful for any help you can offer.