Welcome to TFP.
Where did those test results come from?
Your chlorine, pH and TA are all very low. Are you using Trichlor tablets to chlorinate the water?
Please
create your signature with details of your pool and equipment.
How many gallons in your pool?
Add 5ppm of liquid chlorine to the pool.
Aerate the pool to raise the pH or raise it and the TA.
Yes, you can swim and use the heater. But if your pH is correct it is acidic and can damage a gas heaters copper coils.
The simplest way to raise TA is with baking soda (sodium bicarbonate or sodium hydrogen carbonate). In fact, if you look at the ingredient in the chemical bottle that pool stores sell as “alkalinity increaser”, it is precisely that, baking soda!! And, it is often 2X to 3X the price of the stuff in your grocery store.
Chemicals suggested for raising TA. Their effects are:
- Baking Soda = big TA change, small pH change
- Borax = big pH change, small TA change
- Soda Ash/Washing Soda = big pH change, big TA change.
It is often best to make large TA adjustments in a couple of steps, testing the water after each step, as adding large quantities of baking soda can raise the pH a little and you don't want the pH going out of range.
@mknauss