Simply put, Diatomaceous Earth (DE) are the bones of tiny little animals that lived millions and millions of years ago, diatoms. This DE is used to coat the "grids" inside the DE filter which captures and filters particles as small as 5 microns. When the filter pressure rises, the swimming pool DE filter is backwashed in the same manner as a sand filter. A slurry of DE is put into the skimmer to "recharge" or "re-coat" the grids of these swimming pool DE filters. This type of filter is effective and efficient but a little more expensive to maintain. Some call it the "water polisher" of pool filters.
???? Refer to: Poolspa.com
Yes you can order your required swimming pool filter via the internet. You can go to the website of your pool manufactuer to order the proper filter.
Yes. Running the pool filter pump while swimming has no adverse effects to the swimmers.
The pool filter needs to be "back washed"
Yes. That is how the dirt is removed.
Clean the filter
Backwashing a swimming pool cleans out the sand filter. It reverses the flow to push all the trappings from the filter out.
If you have a sand or DE filter the setting is filter in the case of cartridge filters it is filter as always unless there are other settings for your particular setup.
You can not measure the pressure in a swimming pool. If you mean the pressure on the filter tank gage then you may have to backwash the filter. Talk to your local pool store for instructions as how to maintain a swimming pool and the equipment. Get some education on swimming pool maint. before you get into some real trouble. A pool is not too forgiving for someone without a basic knowledge of pools.
If your water is staying clean it just indicate that there is not much dirt getting into your pool.
The best or highest rated swimming pool filter depends upon the use of the pool because a high use pool needs a higher quality filter. The most popular and therefore rated highest in the popularity sense are the Pleatco cartridges.