It will take two steps to take care of this situation.
First: Use acid to lower the alkalinity to the desired level. This will lower the pH also...so:
Second: Add pH up to raise the pH. This will not raise the alkalinity.
Kind of a pain. Try using soft water to fill if you're just filling a spa. A pool needs too much water, so it'll take two steps.
If you're starting up a spa make sure to wait long enough between adding the chemicals and taking the next test, to allow the chemical reaction to occur. Run the pump(s) (no Air) for 30 minutes then wait at least three hours before the next test.
acid is added to a pool when alkalinity is too high. Take a sample of pool water to your pool shop and have it tested by them. they will tell you what is required.
add acid
24 hrs
add some form of alkalinity booster for sure. bring it too about 110ppm, chlorine has a naturally high pH, but the higher alkalinity addition will stop acidic compounds from attacking the pH any further. depending on how low the pH is though you may have to add a pH booster, take your water into a pool shop for an in depth water analysis.
High Alkalinity will keep your pool water on the higher end of the pH scale, or more basic rather than acidic. High Alkalinity is not terrible but there are two things that can happen. If the water is constantly basic a "scale" can develop. The other thing that can happen is you will notice your pool will get cloudy when you add pH increaser, alkalinity increaser or calcium hardness increaser when either one of those three are on the high side already.
Reduces alkalinity of swimming pool water (softens hard water)
Add rain water this has very low alkalinity
Chlorine will not raise the total alkalinity level in a pool. However, if you are trying to raise the total alkalinity, you can add small amounts of baking soda.
Add more in smaller amounts and test again.
make sure chlorine is is at 1-3ppm, if pH is very low raise chlorine slightly higer than average. shock the pool after and run filter for over night. If pool still not stabilize then add PH high chemical.
Getting a water test at your local pool store would be the first step. Second if it still is low alkalinity add alkalinity increaser. Also can add baking soda is the same stuff. If it says 50lbs you need of Alk. you will need to break that into 3'rds. So every 4 to 6 hours add a third. Have the pump running and you should be good to go after that.
Use a chemical called "sodium bicarbonate" or "alkalinity up" - the dosage is 1.5 lbs for every 10000 gallons and 10 ppm. (So, 1.5*(gallons / 10000)*(ppm increase / 10)=amount) Mix with water in a large bucket and pour it around your pool.