Structure

• Small kiddie pools can be made of preformed plastic. Inflatables use either a rubberized material or plastic. Above-ground pools have steel walls with a vinyl liner inside to hold the water. In-ground pools can be made of different materials such as fiberglass, concrete, shot-crete (which is a blown-in version of concrete) or gunite. Smaller above-ground pools depend on their structure to contain the water, while in-ground versions receive support from the dirt that surrounds them.
  
  

Filtering

• Small blow-ups do not have filter systems, and even if the water is chemically treated, it needs changing every other day. Rubber pools with a blow-up ring generally have small paper cartridge filters and use a 1/8 horsepower pump. They have no skimmer and need leaf and debris cleaning each day. Above-ground pools use either a sand, cartridge or diatomaceous earth (D.E.) filter system. Water flows into the skimmer, through the pump, into the filter canister and back to the pool, completing the cycle with clean, filtered water. These three type of filters range in size to equal the heavier requirements of the larger pools. In-ground pools use the largest versions of these systems, substituting a larger horsepower pump capable of pumping water up to deck level.
  
  

Water Depth

• Small pools can have as little as two feet of water. The next size of the popular rubber pools with blow-up ring is roughly three feet deep. Above-grounds are four feet deep. An expandable liner, if used, can make the center of an above-ground round pool five feet deep. Some above-ground pools offer a hopper, which is a 7½-foot-deep end for a rectangular pool. In-grounds can be as deep as the owner likes if they are free-form, but most have a shallow end of four feet tapering or sloping down to around thirteen feet. Diving boards or platforms are common for pools with these deep ends.
  
  

Chemicals

• The very small pool may use low dose liquid chlorine, but the water needs to be changed every other day because of the lack of a filter. Small cartridge types may have a small compartment for one-inch chlorine tablets. The concern is the viability of the paper filter, which needs constant cleaning or replacement if algae bloom. With each progressively larger pool, the chemical requirements increase accordingly, but so do the choices. Chlorine alternatives such as a number of Biguanide products, copper, salt, mineral packs and ultraviolet systems bring diversity to sanitization and all because the pool size can accommodate it.
  
  

Safety

• As a rule, all in-ground pools must be fenced in to protect against accidental drowning by strangers or unsupervised people, especially small children. The use of safety covers to prevent anyone from falling into the pool when not in use is another good safety measure available. Above-ground pools require a six-foot fence around the perimeter. The pool wall, which is normally four feet, plus the installation of two-foot fencing material that attaches to the top of the wall, meets that criterion. Small pools in the backyard are not usually fenced and require adult supervision. Always check with your municipality when installing a pool to resolve issues about required permits or fencing and any other safety requirements that may be in place regarding a new pool installation.