You can shock overnight - it will go down overnight, and you can even swim in the pool with the chlorine up to 15ppms with a cya of 30 (you can even swim in a pool with higher chlorine). The only thing is you may want to wear an old bathing suit in case it fades a little, mine never has when I swam in my pool with 25ppms, but the chorine won't hurt you. It is better to swim in high chlorine then in anything else that is growing in your pool The faster you get chlorine in the water, the faster it will clear up. You will need 4/1/2 gallons of 6% bleach or 4 1/2 bags of shock to get it to the porper level. I wouldn't use cal hypo, because that is going to add calcium to your water, and the only way to get rid of calcium is to do a partial drain and refill. If your water is clear when the algae is gone, then I wouldn't worry about the calcium, 290 is still in range. Yes, the way to be sure that all the algae is gone is to test after the sun goes down, and early in the morning to see if the chlorine didn't change. Also keep your filter running 24/7 and brush and backwash as needed while you have algae. Good luck