OK.

We won't know for sure till you have the K2006, but your pool is acting like you have (a) a very chlorine resistant strain of algae and (b) high levels of stabilizer. Watch the guide videos, especially the one on CYA testing so you'll be able to get a good reading right away.
http://pool9.net/tk-guide/
http://pool9.net/tk-interfere/
The only preference I had for the 6-way was for finding our your CYA level sooner rather than later.

I scanned back through the thread. Without using phosphates, the only other option you have for mustard algae is higher chlorine. I'd recommend dosing till the OTO has an orange tint. As you push levels higher, the risk of liner bleaching increases. But you really don't have any other options.

You *could* use high levels of copper, but the amounts you'd need (unless you used plain copper sulphate) will cost more than treating for phosphates, and will likely stain the heck out of your pool.

Foamy algaecides don't work against mustard, and polyquat is not much better.

You could use the ammonia based products, to generate monochloramine, but your pool water will become very irritating to eyes and skin. And the clean-up is a mess.

Borates may help somewhat preventatively, but I haven't seen any evidence that they will help once the algae is established. And again, establishing an effective 60 ppm borate level would cost more than lowering phosphates.

Just in case you run into them -- there are some anti-mustard algae products that contain sodium bromide. Do NOT try these; they turn your pool into an unstabilized bromine pool for an unknown period of time. Using them will cause your chlorine use to skyrocket and will accomplish nothing you can't already accomplish by raising chlorine levels directly.