Crazy high cya and chlorine levels....

I just bought a home with an inground, 20k gallon pool, uses a pentair fns plus DE 8 grid filter with a pentair whisperflo pump( not whispering) and the pool test kit I just bought shows the chlorine at a dark orange color, and the ph is lighter than the scale of comparison, also the cya test is so clouded that the little black dot disappears waaaay before the 100 ppm line, like and inch or more before it, so obviously way too high. I'm new to pools so I'm kinda lost on what I'm supposed to do to get the water back into balance, none of the tests are reacting correctly due to maybe high acid and chlorine? Please help. I'm interested in the BBB method but wondering how to start? Do I have to drain the pool? It's been raining like crazy and I'm worried about draining and the surrounding ground water moving the cement.... also, is it normal to have mass worm suicides? Like seriously hundreds of them every rain.... I'm dumbfounded.