While pool chemicals will always get sole credit or sole blame for water clarity or lack thereof, they are not the single contributing factor; they are not even the main factor. Yes, pool chemicals do affect (either positively or negatively) water chemistry, and yes, optimal water chemistry does help promote or deter water clarity, but the pump, filter, and plumbing specifications are the main components for attaining water clarity. Proper circulation (via the pump) and filtration (via the filter) greatly – greatly – assist your pool chemicals with maintaining highly sought-after water clarity. Additionally, proper plumbing sizes (in terms of diameter for plumbing pipe) and specifications greatly - greatly - assist your pump and filter. Of course, this is all contingent that the plumbing runs and sizes, as well as the pump and filter, are all PROPERLY-SIZED to work together, given the number of gallons of water your pool holds and other specifications.
Most pool owners still have a conventional horsepower-driven pump; unfortunately, many of you have an improperly-sized pump, primarily too high of a Horsepower. And, regardless of the type of filter, many of you have an improperly-sized filter, primarily too low of an Effective Filtration Area. To make matters more difficult, many of you even have too small a diameter of plumbing pipe, which restricts circulation and filtration. Even the most renowned pool chemical expert in the world would struggle to maintain optimal water clarity in these conditions.
As a pool owner, the smartest money you will ever spend for your pool is to properly-size (and ultimately re-engineer) the plumbing, pump and filter. As the plumbing, pump and filter are properly-sized, your pool chemicals will be better distributed for optimal water chemistry, which will help with water clarity. The better distributed the chemicals, the less likely you are to battle algae, cloudy water, discolored water, and other detriments to water clarity.
Of course, adhering to a routine maintenance schedule will also help with water clarity.
The pool chemicals will always get sole credit or sole blame for water clarity or lack thereof, but with improper equipment, plumbing, and maintenance, even with the best pool chemicals, you will find it more difficult to attain and maintain water clarity.
You can read the Pool Manual for additional information about pool chemicals, water chemistry, water clarity, properly-sized equipment and plumbing, and adhering to a routine maintenance schedule.