By any chance, are you aerating your water? (Ex. -- is your return jet pointed upwards creating bubbling on the surface?) if so, aim the jet down.

Go ahead and add some more baking soda. Baking soda shouldn't change the pH much but will increase the TA. Add a couple of lbs. at a time until you get it up to about 110 or so. After each addition, wait a few hours, retest TA and then redose with more baking soda until you get it to the target. Then, add a little muriatic acid slowly in front of the return jet. Wear gloves, glasses, pour close to the surface of the water to avoid splashing, stay upwind of fumes. Test pH a few hours later and redose with more acid until you get to about 7.4-7.6.

When you are adding the baking soda and then the muriatic acid, you do not have to wait more than a couple of hours between additions of more.

Hope this helps.