Quote Originally Posted by knarf#2
I have a 15,000 AG and here are my test results from today. Probably should get the PH down a bit. How much M. Acid should I use? Anything else?
PH 7.8
TC 15
FC 15
TA 180
CYA 100

Thanks in advance
As Sully said, until your pool clears that should be your main focus. I didn't realize you had an algae problem and if you do, then you aren't at the shock levels according to Ben's Table which says you should maintain 25 ppm FC when your CYA is 100 (in fact, you may need even more, but at least get to 25). So first get your chlorine up and that should get you to clear faster.

Nevertheless, with your numbers, to get the pH down to 7.5 you need to add 27 fluid ounces (3 cups, 3 ounces) of Muriatic Acid. However, your TA and CYA are both quite high and at some point you should do a partial drain and refill which will lower TA and CYA (and FC, TC, CH). Again, you can do this after you pool clears.

Do you know why your TA is high? Is your refill water high in TA (you can test it if you don't know)? The high TA will cause your pool to outgas carbon dioxide at a more rapid rate and that makes the pH rise. Essentially, your pool is over-carbonated. After you solve your algae problem, you should first do the partial drain and refill to lower both TA and CYA. You should try and get your CYA down to no higher than 50. If after the partial drain and refill your TA is not down to 100, then follow Ben's Procedure for lowering TA. You can see from the following chart that you can't simultaneously maintain lower pH and high TA -- the pH will tend to rise as long as your pool is exposed to air (i.e. not covered). Increased aeration (splashing, wind, bubbles, etc.) make the pH go up faster.

Richard