Brian,

If you truly have mustard algae, apparently it's pretty resistant but can be cured with high levels of chlorine applied CONSTANTLY to your pool 'til there is no longer any sign.

I suggest you only do this with Clorox...no more powder ("shock"). Bring the Cl level up to 14-18ppm and KEEP IT THERE until your pool is clear......that may take several days but it will probably improve by Saturday.

Now, you can KEEP IT THERE only by testing and adding Cl at least twice and three or four times a day is better. If you do not have a test kit to help you do this (your test results look like pool store results) it is going to be difficult (virtually impossible). See if you can find the HTH 5-way kit (Walmart). Otherwise, you may have to put some wear and tear on the hinges of the pool store door.