I have had this pool for over 7 years with no problems. It is a 24 foot above ground pool. Every year I never have any problems, the pool is usually brownish when I first take the cover off. Then I always put algaecide 60 in it, and use powder shock to raise the free chlorine level to around 7.5PPM. Then I run the filter filter pretty much 24/7 for about 4 days, backwashing every 12 hours. When I backwash the water coming out of the backwash is always very green, and then after about 4 days my pool will be clear. This year is a different story. So here are my stats for water just so you know.
Free Chlorine 6.5
Total Alkalinity 70 PPm
I had the water tested for phosphate and hardness at the pool store and they said it was fine.
I have a 1HP pump with a 19 inch sand filter that holds 175 pounds of sand, it is a proline, which is pretty much a hayward setup.
All lines are clear, skimmer basket is clear, pump basket and impeller are clear.
So as I said I put in my algaecide 60 and chlorine in, and the water turned from brownish to an aqua blue green and is cloudy. I have had the filter running for about 14 days on and off. Also there are no leaves or anything in the pool. The water never got clear and never had to be backwashed, and when I did backwash the water came out of the backwash clear.
So I figured I needed new sand cause the sand in the filter was about 7 years old. I changed the sand by using a shop vac, and the laterals in the tank looked fine, I put 175 pounds of new filter sand in the tank. I also put in a bottle of clarifier. The pressure in the tank is around 7-8 PSI and it seems as though the water is just not being filtered. It has run for at least 72 hours with the new sand and there has been no change at all. Water is still cloudy greenish blue. The water never needs to be backwashed, the pressure in the tank never rises, and when I do backwash, the water coming out is clear, not green as it should be.
Could it be my selector valve has gone bad? It is not leaking or anything, but I am running out of ideas here. Does anyone have any idea what the problem might be? Please help.