For the last three years my pool has been clear as clean glass. Even at night with a 400 watt underwater light shinning you have to look closely to see any particles. Now the pool has clouded up. I can still see the main drain, but the water is turbid looking. I don't think it's an algae problem because the cloudiness is white there is no green or yellow that I can see in the water or on the walls or bottom. The water chemistry seems in line and I keep a close check. This morning's numbers are:
The cloudiness started about two weeks ago and I initially thought the filter just needed back washing. The filter was very dirty and it took longer than usual to get the back wash clear. After three days the water was still turbid so I back washed again and the filter was not dirty at all. Next I tried adding 1 cup of filter aid (diatomaceous earth). The filter plugged off almost completely in about 1 hour. I back washed again and added 1/4 cup of filter aid and the filter plugged again in about an hour.
The filter is a Hayward S-244T sand filter that was installed in 1991. As far as I'm aware the sand has never been removed and the internals inspected. The filter has never operated the way I thought it should. When it is clean just after a back wash the pressure is a constant 24 psig. If it gets very dirty the pressure might get to 27 psig, but I normally back wash when the pressure gets to 25 or 26. I can't find the exact pump curve for my pump (Sta-Rite Dura-Glas, Model MPRA6F-148L, 1.5 H.P., single speed)any where, but the generic curves say the pump should put out a minimum of about 80' head or around 35 psig at dead head.
One explanation I can think of is that some of the laterals are plugged off. If one or more laterals were plugged or several are partly plugged that might account for a high initial discharge pressure. It might also explain the loss of filter efficiency because some portion of the filter bed above the plugged laterals would not be used. Another explanation might be the flow rate is too high for the filter. The filter name plate lists the maximum flow as 60 gpm, but since I don't have the pump curves and cannot measure the flow I don't really know if that is the problem or not. I don't have any valves on the discharge of the pump or filter and I don't want to throttle the pump suction valves so I'm kinda stuck. My next option is to take the filter apart, remove the sand and inspect the internals. But before I do that I wanted to get input from some of the knowledgeable people here - have I overlooked any thing and is there something else I can do before dismantling filter?