I'm not positive, but I'll be willing to bet the "shock" they sold you was sodium dichlor--which actually is acidic and will drive your pH downward. Adding Borax will get the pH up into the 7.0-8.0 range, where it belongs--and this is a critical thing...if your pH is lower than 7.0, your water is very acidic and will damage your liner, if you have a liner pool. You need to get a good reading for pH, and start adding Borax immediately to get the pH back up above 7.0. When your pH comes up, it is likely that your TA will come up, as well. Do you use trichlor tabs for chlorination? They are also acidic and will drive pH down. They also will substantially increase your CYA, and I see that it is very high,.

Your chlorine fluctuation and algae blooms are likely because you're not keeping your chlorine high enough to keep the algae gone, and so you're continually fighting an algae bloom (you're definitely fighting something with a FC of 0 and a CC of 4). With a CYA of 100, you need to be keeping your chlorine at an absolute minimum of 8 ppm, but now that something's in the water you need to shock the pool. For a CYA of 100, that shock level means you need to raise your chlorine to 25 ppm, and hold it there by testing and adding more chlorine, until you can go overnight without losing more than 1 ppm of chlorine. When you get to that point, you can let the chlorine drift back down, but not below 8 ppm.

Ignore the phosphate level--it's not really relevant to your situation, and it's just another way for the pool store to convince you to buy something you don't need.

Welcome to the forum!