If your pH is too high, your Alkalinity is NOT too low. You need to lower your Alkalinity until pH is correct. Forget the range for Alkalinity, it means nothing. Read the top link below (Water Balance section). BTW, what is your TA?
Artic is wrong, which doesn't surprise me. If your Calcium is 20 ppm, you need to raise it to at least 100 ppm. Again read the Water Balance section below.
That dealer is talking BS, which doesn't surprise me. Your Calcium should be around 100-150 ppm. If it's 20 ppm, that's way to low. My advice is to add Calcium, and stop talking to dealers.
I don't think I explained this well - what happens is that when my TA reading is fine, my PH reading is often high. So, I add PH down and the next day the PH is lowered but then my TA reading is lower than the acceptable range. So, I add buffer to raise the TA and the PH goes up as well. I will have to get a proper test kit - as you can guess all I have been equipped with is test strips and, driving 30 minutes to the dealer for a water test can;t happen every few days! I will get my water tested tomorrow and post. Regardless, I will add something to rasie CA as well.
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