(Disclaimer: Read and follow your equipment manufacturer's recommendations! Every filter and every installation is unique. Do not attempt to complete work that you are not qualified to complete. These are general ideas and this information does not constitute specific advice to be acted on prior to consulting a professional.)
A couple thoughts...
1. Don't change your sand just to change the sand.
2. Is there sand around the returns in the bottom of your pool? If your sand is 10+ years old, it may have become rounded and worn and it may be squeezing through the grooves in your laterals and washing back to your pool. Sand in this condition not only makes a mess in your pool, but it also is not as effective at trapping and filtering contaminants. The small, jagged edges of each grain of silica sand is what traps and filters out that unwanted debris.
3. Has your pool become unexplainably cloudier over time with 10+ year old sand, with no other environmental or operational changes to explain the change? Again, the sand may be rounding off. To avoid the trouble of taking off the access hatch, if you hold your a strainer (preferable) or even your hand or fingers under your back wash discharge waste line during backwash (wash your hands afterwards), you can often grab a few grains of sand and take those to be inspected under a microscope. A trained professional can evaluate the shape of the sand and advise if replacement is necessary.
4. If your water clarity is suffering in a hot water pool or spa, we have also seen sand congeal and stick together like molasses. Over time it can became hard and brittle to the point where it actually needs to be chipped out with a hammer and chisel. If your filtration just doesn't seem to be keeping up, the sand could be the culprit!
5. Another situation where you may be replacing sand : a broken filter lateral. The filter laterals (see picture below) sit inside your filter at the bottom of the sand bed. They have very small slits or grooves cuts into them that permit the filtered water to pass through and return to the pool, but the sand is too large to fit through and is therefore kept in the filter. If these laterals become worn out over years, or if one breaks with even a hairline crack, you will often see a lot of sand on the bottom of your pool right around the returns. In this situation, there is no easy way to repair the lateral. Typically, the sand must all be removed, the lateral replaced, and then the sand must be returned.
Video and Pictures of a Recent Filter Sand Replacement
A multi-use indoor pool was recently experiencing issues with filtration. 160 cu. ft. of sand media was removed and replaced from a 64 sq ft filter.
After draining the system, we popped the hatch.
View inside the hatch.
Influent pipe at top of filter with diffuser plate underneath.
Quick video of inside of filter.
Call in the vacuum truck to suck out the sand. These guys worked on that filter for several hours. We removed the sand down to the laterals. In a small commercial or residential pool ... a wet-dry vac will do the trick!
We removed all of the sand down to the laterals. Not visible here, but in this filter there is actually gravel layered underneath the sand. We left the gravel in place as it was fine. Once we got to this point, it was dumping bag after bag (3 pallets worth) of #20 silica sand back into the filter. The project ended in success. The previous filtration issues were no longer present.