My test kit doesn't actually read higher than 5 but I keep it MUCH higher. I shocked using 6-8 bags of 62% calcium hypochlorite over 48 hours in addition to HTH algaecide initial dose, then continual pucks in the skimmer. I have a sand filter. The ph is 7.6. The water in the pool and the pool floor stay perfectly clear until I turn the filtration on. Is the stuff living in the system?