Woh!! Full stop! Hold on there... Stop! Do not pass go!
Your water with a 19 KH will require a tremendous amount of acid to lower this.
No way is gypsum ever strong enough to lower your pH with a KH as high as 19.
The 29% phosphoric acid concentrate of Botanicare would make a dent, but you will need quite a bit of it to burn through 19 degrees of KH before your pH starts to lower.
The best way for me to describe what is happening here is to use my mattress example. The mattress is the water. The springs within the mattress is the KH. The act of "jumping" on the mattress is the acid. Water with a high KH is like a mattress with very strong springs. With strong springs, then the more you bounce on the mattress. The more you jump on the mattress, then the more the mattress springs lose strength, allowing less bouncing. This describes your situation perfectly
@Lindasue As you add your acid, you will notice the pH go down for a few hours, but, after a few more hours, you will then notice the pH bounce back up to where it was in the beginning. This is due to your quite high KH.
As you add acid, then there is less KH, but takes a tremendous amount of acid to lower KH.
Do not use phosphoric acid. The salt of this acid is phosphates and you do not want to add more phosphates to your pond water. This will create a massive algae explosion for you.
Muratic acid, also called pool acid or hydrochloric acid, is more suitable, but this is incredibly caustic and dangerous!! Be sure to wear a gas mask and a chemical suit. I know there are fella's that do not bother with these safety precautions, but all it takes is for one misplace drop or inhalation of fumes and you have a serious chemical burn or pass out.
Do not use these acids unless you are fully comfortable to do so. Personally, I would recommend you to avoid these acids
@Lindasue Also, look into using liquid test kits. Test strips are nice for a quick test, but they are not very accurate at all. Test strips act like a fire alarm in that the strips sends an alert to tell you if something is wrong. Once you know something is wrong, then you need to pull out your liquid test kit to get better details.
Your pH should actually not be as high as 9.0 if your GH was at 26, but, since I am guessing this is not city water due to the high KH level, then most likely there is something else in the water influencing the 9.0 pH.... but... Do a liquid test kit test first on your pH and KH before deciding to do anything else.
