What is the best filter media for my sand filter?
There are a few things to consider when making a decision on what filter media you are going to use in your sand filter. Cost. Effectiveness. Longevity.
Isn’t sand the best filter media to put into a sand filter? It seems like the answer would be obvious; of course sand goes in a sand filter, right?
Before filtering through your different options, here’s a quick review of filtration basics. The size of the suspended particle removal is generally measured in the unit of a micron. The picture below uses table salt as the reference at 100 microns. There are approximately 25 microns in 1/1000 of an inch.
Now let’s talk the major players in filtering media.
Silica sand is the oldest of the filtering medias. Not all sand is created equal and if you are going to replace your old media with sand, silica sand is the way you need to go. Number 20 silica sand will filter down to 20 microns. As you can see from our chart above it will take care of most suspended solids in the pool water. One thing to keep in mind is that the dreaded unicellular green algae are 5-10 microns in diameter, not including the flagella (add an extra 10-30 microns for the flagella). Volvox can get huge–up to 500 microns (half a millimeter–visible to the naked eye). So, silica sand will get some algae, but if you have an outbreak it will be necessary to use a clarifier to group the algae cells together in order to get it caught in the filter. The other thing you need to know is that the average silica sand will last 3-5 years depending on pool usage and the foliage around the pool.
We are finding that using a glass media not only gives you superior filtering for better water clarity, but it lasts longer.
Natural zeolites form where volcanic rocks and ash layers react with alkaline groundwater. It is also produced commercially. Without getting too technical, zeolites are microporous and the voids in the media are ideal for catching debris flowing through your filter. Zeolite boasts to filter down to 5 microns clearly making it a superior filtering media to the silica sand. But there are a couple things to keep in mind if you’re considering zeolite as a filtration media. When you put it in your filter you will notice a lot of dust. This dust will run out into your pool after you install the zeolite for the first time if you do not do a thorough backwash first. I recommend backwashing for 3-5 minutes, running the rinse cycle for a minute and repeating the process before going into normal filter mode. It is not the end of the world if the dust gets in into your pool, it just takes a few days to filter out so it is nice to avoid it if you can. You only require half as much zeolite as your normal silica sand. If your filter requires 300 lbs of silica sand, you only need 150 lbs of zeolite. Zeolite is also supposed to last 5-7 yrs as opposed to the 3-5 of silica sand. Zeolite is more expensive but if you are having the media changed by a pool pro; the money you save on labor because you don’t have to change it out as much makes up for some of the expense. Also, keep in mind your pool water will be cleaner with fewer suspended particles.
The last option we’ll filter through is recycled glass.
Say what? Glass? To filter pool water? Well sure! Not only is it environmentally friendly, but it actually works. We are finding that using a glass media not only gives you superior filtering for better water clarity, but it lasts longer. Recycled glass is compatible with all sanitation systems. One advantage is that we are finding glass needs to be cleaned less frequently. This saves on water and chemical costs and that adds up when you look at the annual numbers. The glass particles have a slightly negative charge which attracts smaller particles allowing it to filter between 5 and 10 microns. The other thing that separates this media from the other two is that sand and Zeolite only use the top 6” of the media bed to filter out debris. Glass media uses all of the filtering media down to the pea gravel. There are companies such as VitroClean who tout that the recycled glass can last up to 10 years. Is this a more expensive form of filter media? Yes. But if you look over the course of 10 years maybe not. If you are using silica sand or Zeolite you may be changing that media 2-3 times over the course of 10 years. The labor cost alone will more than make up for the initial cost of recycled glass.
Is there are wrong choice when picking out your next filter media? Nope. That being said, filtration technology has come a long way and it might save you a pretty nickel to take a look around before using the old standby on your next media change.