Interesting. That pretty much rules out borates as having much impact on mustard algae. It's also amazing that you're having recurrent algae with FC=20 and CYA only 30 ppm.

I have to say, that while I'm sorry for your problems, I'm glad for the opportunity to test this out. The fact that you have no phosphates in your tap water certainly makes things easier. You will need to practice extreme vigilance in what chemicals you use, and avoid using ANY products made by United Chemicals, as well as most stain/scale products. You probably want to avoid clarifiers, flocs and any other 'enhancement' products.

But even there it will be interesting to track your phosphates, to see what makes them rise, after you lower them.

Thanks so much!