How much did you drain? Does the shock that you have list sodium hypochlorite as the ingredient? If so, you can go ahead and use it in the pool, but I doubt very seriously that it is still 10% after that much time. Unless you did a total drain and refill (and I hope you didn't!!!), you do NOT want to use the trichlor tabs. Just use bleach. If you use bleach, you just have to test it every evening or at least every other evening and add a little bleach. How much to add depends on what your cya level is. I usually check it every evening and add a little bleach. It takes me no more than 5 minutes at most.