I agree with Ben:

BTW, if your pH is 6, there is absolutely, positively NO WAY you should add pH Down! That's a powdered acid and the pool is already seriously acidic! You do NOT want it more acid. If you goofed and it's actually pH Up! they recommended, then you should know that Arm & Hammer Washing Soda (in the yellow box in the laundry section) is EXACTLY THE SAME CHEMICAL as pH Up!

BUT---as Ben says, what you NEED is chlorine, and that is easiest to add by adding plain, unscented, bleach. And, without proper testing, anything else will mess things up AND none of the things they told you to add actually kills algae.