Sand Filter Problems

Problems with sand filters can be difficult to troubleshoot because they are not as clear cut as a torn grid
or cracked manifold.  If the sand goes bad, it often cannot be detected by simply looking at it.  Here are some of the problems that can occur with sand
filters.

Problem:  Bad Sand

Symptom:  Water Clarity Problems (in spite of good flow)

This happens when the sand appears to be in good shape, but simply will
not filter out debris in the water.  If there is a problem with cloudy water, the first step is to test the water carefully and totally eliminate water
chemistry as a possible cause.   Check the backwash valve also to make sure that water is not simply bypassing the filter.  The next step would be
to change out the sand in the filter.

Problem:  Clogged or Dirty Sand

Symptom:  Short Filter Cycles

This happens when the filter goes less than a day between backwashing.  If this is
the case, then either the filter is undersized, or the sand in the filter is clogged with oil and dirt.  It is not unusual to find the sand in the filter to
be “muddy”.  When this happens, the effective filter area is greatly reduced since water does not flow easily through non-porous areas.  A
filter with a normal surface area of 4.9 square feet might be reduced to an effective filter area of 1.0 square foot or less.  This will cause serious short
cycling to take place.  The solution would be to change out the sand in the filter.

Problem:  Bad Laterals

Symptom:  Sand Returning to Pool

If there is a large amount of sand being dumped into the pool through the pool returns,
then bad laterals could well be the cause.  The pool operator will need to remove the sand in the filter and check the internals for breakage.

Problem:  Missing or Displaced Air Relief Tube

Symptom:  Sand Returning to Pool

If there is sand being dumped into the pool through the pool returns, particularly
after backwashing, then a displaced air tube could be the cause.  The filter will need to be opened up to see if the air tube is properly secured in place.  
This can generally be done without removing all the sand in the filter.