Another Update:
I hesitate to post this because I don't want to upset anybody on the forum. I absolutely love this site and it has saved me money, time and heartache. But...my husband demanded that I change course, or the pool was to be covered over for the winter ASAP.
Here’s a recap of the journey so far.
My enemy started off looking like patches and streaks of sandy dirt (which is what I thought it was) while the water looked like glass. MY FC and CC would pass the OCLT, but I would see either light brown patches or white sandy patches on the floor and in the seams. There would be what looked like sand in the indents on the steps and on the skimmer surfaces. It started in the shallow end but did end up in the deep end also. It seemed to brush up easily for a while, but then the vinyl started feeling somewhat slippery under the pool brush and some strange stuff started showing up that was difficult to brush or even vacuum. I have brushed multiple times a day, vacuumed to waste several times, have taken the ladder out of the pool, and all equipment stays in the shallow end receiving treatment when not being used. I have done this since mid-May.
Okay....here it goes. I committed a TFP sin at the demand of my spouse.... I researched and decided to use a chelated copper algaecide. I was scared to death to use it. The only other time I've ever added anything other than the basic minimal to our pool was Green to Clean for our first green algae outbreak (before finding this site). I have been keeping my FC at mustard algae SLAM level, I started off with a pH of 7.3, have been brushing at least 2 times a day (brushing any recurring patches in between those 2 brushings), and have been running my VS pump on 2400 - 2900 RPMs 24/7. Those were also things that I was doing pre-algaecide. There has been a TON of rain here since starting the treatment, but within 12 hours I noticed that brushing created an unbelievable amount of "dust" clouds (even from the walls) and my pool was difficult to see into. And....it started to use up the chlorine. The first day resulted in a lot of light sandy colored patches. It almost seemed like it was fighting back.... weird, I know. Yesterday, the pool was still cloudy, but I could see the floor better. Also, the brushing created sparse white dust clouds with only a few darker ones. The recurring spots had decreased tremendously and were only white dust. Today is the 3rd day. My FC is holding well and there is only the tiniest amount of white in one spot of the shallow end. Also, the pool water is clearer. I think this strain needs a 1-2 punch to be defeated. This is the 1st time since opening that the cycle appears to be different. I don't know why but it seems to be working.
Also, I have not put the Dolphin pool cleaner in yet this season because I didn’t want to expose it to what was in the pool and risk re-contamination by using it.
In the future, I plan on adding a polyquat 60 algaecide on a weekly basis and I will shock with chlorine once a week. Pre-mustard algae, I just balanced chemicals, ran the SWCG and put the Dolphin cleaner in the pool 3 times a week, which worked well.
I want to thank those who have offered me advice.
I will continue to update and hopefully, will not need to seek further assistance with this particular issue.
And....I am still a firm believer in the TFP method and it will always be my first choice.