Yes, I would drain and refill first - try to get your cya down to 50 if you can, but 60 to 90 is ok if you want to run high chlorine. We usually recommend 35 - 50 on this board. Next add the muriatic acid there is the bleach calc on this forum, Here is the link:
http://www.hal-pc.org/~mwsmith2/BleachCalc262.exe
You can use this to figure out how much bleach you need, how much acid for ph, or borax and others - in the upper left corner it says more calcs, click on that and you will see the different calculations you can use. If you go to settings make sure it is on the imperial so you get the calcs in gallons. Bring your ph down to 7.2. The ph will not register lower right away, so don't add any more than the calc tells you, it will show up later.Five minutes after adding the muriatic acid you can add the sequestering agent - like I said, add a little more than the bottle says. You can add the bleach right after - enough to bring the chlorine up to shock level. Brush the pool and Keep the filter running 24/7. Keep checking the chlorine and bring it back to shock level until you hold the chlorine overnight, then add 2 days just to be sure. You want to make sure all the algae is dead. You should see a noticable improvement in the water color after you hit it with the bleach in a couple of hours. Your water may get cloudy from the sequestering agent and the dead algae. Just keep the chlorine up, and the filter running and your water will clear up. Keep me posted on your progress. Once you take control of your own pool, you will find it much more enjoyable, and you will get to know how your own water is - everyone's is a little different! You will get used to how much chlorine your pool uses, and you will spend hardly anytime on pool care.