Sanitize or replace old camper fresh water holding tank?

My clipper is a 75. It has the original fresh water tank. When I bought it, I add the chlorine granules (1 tsp) in a small bottle of water, I filled the fresh water tank about 1/4 up, added the chlorine/water mix, then filled the rest of the tank. I let it sit for 24 hours. Then I turned on ALL the faucets and let all the water run through the system. Then I re-filled the fresh water tank with straight water and went camping. Like Turtle n Peeps, I'm not dead yet.