Ph up / down

I dont understand how if ph fluctuates people correct using ph up and down. Thought the two couldn't be mixed!?!? DWC

if your ph is low you add up. if ph is high you add down. no mixing required

What's the problem? use it as it says ph up, raises you ph, ph down, lowers your ph. never mix.

Take some ph down and mix it with ph up and see what it does...