You just need to get your TA to above 50 ppm. And pH in the 7's. You will most likely need more than 5 lbs of soda ash. I would suggest getting 7lbs of baking soda too. Once you get some reading of TA, you will switch to baking soda to raise TA.
You need to do this now. Your water is destroying your liner and heater. Quickly.
Dissolve the soda ash in a bucket of water (may need to do a few batches). Pour in around the pool with pump running. Wait 30 minutes and test TA. If still 0, add another 5 lbs of soda ash. Once you see a TA reading, test pH and use baking soda to raise TA to between 50-80 ppm.