Are Sand Filters Good Filters?
So you’ve heard that Sand Filters have a few advantages over Cartridge or D.E. right? Well, that’s both correct and incorrect. Let’s quickly go over the details.
A Sand Filter is definitely easier to clean on a regular basis. The reason why is that you don’t have to take it apart to clean or backwash it. They all come with either a “Push Pull” valve or a rotating “Multi Port” valve.
The “Push Pull” valve works like it sounds. You stop the pump and “Pull” up on the handle of the valve after unlocking it. Then you turn the pump back on and water will run in reverse through the filter pushing dirt out through your discharge line (a hard or soft hose that runs out to an area of your yard or a drain) until the water is mostly clean (usually 2-3 minutes). You can then turn the pump on and off for about 20 second intervals a few times to get extra dirt out. Then after turning the pump off you “Push” the valve back down and lock it in place.
The “Multiport” valve rotates to different modes while the pump is off. Usually you push down on the short handle and then rotate the valve. There are usually Filter, Backwash, Rinse, Waste, and ByPass modes. Filter mode is obviously used for normal filtration and is where you will put the valve after you clean the filter. To clean the sand you will shut off the pump and rotate the valve to the “Backwash” position. Turn the pump back on until the water runs clear (usually 2-3 minutes). Then turn the pump back off and rotate the valve to the “Rinse” position and run the pump for 30 seconds. Turn the pump back off and rotate the valve back to “Filter”. You have the option of running the water through the filter a couple of times by repeating these steps two times.
You only need to backwash your Sand Filter when the pressure on the gauge goes up 8-10lbs (usually every 2-3 months). With that said I strongly recommend that you backwash more often. I would suggest that you do it every month regardless of filter pressure. This is because I am trying to help you avoid one of the biggest disadvantages of a sand filter.
If you wait too long to clean a sand filter, dirt will pack itself into the sand so much that when you backwash it will not all come out. After a while the water will find the path of least resistance and develope channels around the sand essentially bypassing the sand completely. At this point you have a filter that doesn’t filter the water. The only way you can fix this is to try a degreasing agent designed for sand filters or remove the small top of the filter and scoop out the old sand and replace it. Trust me, you don’t want to do that because it is not fun.
So to sum up the advantage of a Sand Filter, it is very quick to clean and you don’t have to take it apart. Unfortunately there are several disadvantages.
The first disadvantage was talked about above. If you don’t backwash the filter often enough you will cause “Channeling” of the water around the sand instead of through it. This will dramatically reduce the effectiveness of your filter.
Second, sand filters usually have a very low flow rate. This means that your pump can only push a certain amount of water through the filter at one time and that amount is very low. A low flow rate means that you have to run your pool pump longer to accomplish the desired one turnover per day (all of your pool gallonage passing through your filter once per day). This means more money spent on electricity every month.
Third, sand filters only remove larger particles at first and then only slightly smaller particles over time. They will remove particles down to about 20 microns in size. We can see down to about 30 microns and a human hair is about 60 microns thick. This means that there are somewhat large particles still in your pool water at all times. This can mean that you will have more issues with algae and more chemical usage because those particles are food for algae and chlorine will try to attack them.
Lastly, sand filters do not fully backwash with most residential pool pumps. Depending on the horsepower of your pool pump, you may not generate enough flow during the backwash cycle to fully disrupt and clean the sand. Most of the time the sand will stay where it was instead of moving around rapidly as it would with a large commercial pump. This is why you will see sand filters being used in large commercial facilities like water parks or resort hotels. They all have such a high bather load (the amount of people using the pool) they need to backwash sometimes hourly. This is usually automated and the pumps are very powerful creating a very nice backwash.