Just remember that there are two primary purposes of running the pump. One is to move the pool water through the filter to remove suspended particles faster than they get introduced into the pool. This helps to keep the pool from getting cloudy, but putting water through the filter doesn't have much to do with preventing algae unless the algae is already clumped or consolidated, say with a clarifier (PolyQuat is both an algaecide and a clarifier). Generally speaking, a pool should have at least one turnover of water through the filter each day (24 hour period), but this greatly depends on the amount of junk that gets into the pool. Pools that are usually covered may be able to get by with just 1 turnover or perhaps a little less while those that are uncovered and have higher bather loads or junk getting into the pool may require 1.5-2 turnovers. Water clarity is the easiest indicator to know whether the pump isn't being run enough (or at high enough speed to get the number of turnovers). In an SWG pool, having water run through the SWG helps kill free-floating algae as a portion of the water gets exposed to extremely high disinfecting chlorine levels so for this purpose, more turnovers per day are better (but not necessary if chlorine levels are maintained and circulation is good -- see below).
The other purpose of running the pump is to move the water around in the pool -- that is, to circulate it. This is to thoroughly mix all chemicals and to redistribute chlorine in case it gets used up locally in one area of the pool. Without this circulation, you can have chlorine in the pool and still get algae if for whatever reason some algae gets started in one area (say, introduced from a pool cover) and then the chlorine in that area gets consumed so now with zero chlorine in that area the algae can really take off. With a cover, the circulation just below the cover might be worse and if UV is able to get through the cover, then the chlorine level just below the cover could get close to zero.
Running the pump for 5 hours is normally too low. Even if a slower pump speed were used so you still had only around 1 turnover, having the pump on for a longer time of at least 8 hours would help prevent algae from growing by making sure chlorine got distributed everywhere. Even splitting up the time to be some during the day and some at night helps and can be done using a lower-speed pump which also saves a lot on electricity costs. Generally speaking, the only time you can't use this approach is if you solar-heat your pool since that requires higher flow rates. In my own pool with a variable-speed pump (Pentair IntelliFlo), I have it set to do one turnover at 26 GPM over 10 hours though on sunny days there is around 4-6 hours running at 48 GPM through the solar panels so I get more than one turnover on those days. If I didn't have the solar panels, I would have the pump running at an even lower GPM over a longer period of time, possibly split into two pieces for day and night.
Richard
The other purpose of running the pump is to move the water around in the pool -- that is, to circulate it. This is to thoroughly mix all chemicals and to redistribute chlorine in case it gets used up locally in one area of the pool. Without this circulation, you can have chlorine in the pool and still get algae if for whatever reason some algae gets started in one area (say, introduced from a pool cover) and then the chlorine in that area gets consumed so now with zero chlorine in that area the algae can really take off. With a cover, the circulation just below the cover might be worse and if UV is able to get through the cover, then the chlorine level just below the cover could get close to zero.
Running the pump for 5 hours is normally too low. Even if a slower pump speed were used so you still had only around 1 turnover, having the pump on for a longer time of at least 8 hours would help prevent algae from growing by making sure chlorine got distributed everywhere. Even splitting up the time to be some during the day and some at night helps and can be done using a lower-speed pump which also saves a lot on electricity costs. Generally speaking, the only time you can't use this approach is if you solar-heat your pool since that requires higher flow rates. In my own pool with a variable-speed pump (Pentair IntelliFlo), I have it set to do one turnover at 26 GPM over 10 hours though on sunny days there is around 4-6 hours running at 48 GPM through the solar panels so I get more than one turnover on those days. If I didn't have the solar panels, I would have the pump running at an even lower GPM over a longer period of time, possibly split into two pieces for day and night.
Richard