Sand Filters 101
HOW IMPORTANT IS SAND QUALITY?
Sand filters are a common choice for many pools due to their user-friendly method of operation. Precisely because of this ease of use, it is also very easy to overlook the importance of the main component of the filter, namely the sand itself! It is for this reason I’d like to focus more on the actual sand and less upon physical and mechanical issues. Factors such as the type of sand, granule size, how often to change, and best practices for changing the sand are not often given much thought, and because of this, problems may happen that need not occur.
The topic of filter sand is deceptively simple. There is a lot more to it than at first glance. For this reason, this is part 1 of a 3-part series on the subject. In this blog we’ll cover the following: the type of sand; why you should change it; how often to change; and problems related to condition of the sand.
First, it’s important to know how the sand in your filter works. Sand may look pretty simple, however examined under a microscope the right kind of filter sand will show sharp edges on each granule. Taken together the edges work to trap and remove unwanted debris from your pool water. The more edges you have and the sharper those edges are, the more debris you’ll remove from the pool!
At E-Z Test Pool Supplies years of practical experience have taught us to sell and use white silica sand only. Although the cost is slightly higher than the cheap stuff we recommend Mystic White II™ from US Silica for residential filters, and for good reason. This sand made of high quality ground quartz (a form of silica), is consistent in granule size and finer than most sand (.44 to .49 mm). This effectively translates into more sharp edges to catch debris and finer overall filtration well worth the extra few bucks.
So you’re probably thinking, “Once there’s sand in the filter, why would I EVER need to change it? You can’t break sand, right?” (And yes, being in retail does give me mind-reading experience!) Sand does not so much break as it wears out over time. I call this the “river rock effect”. We’ve all seen rocks in a river worn smooth over time by the action of the water flow. It’s the same principle happening much more quickly because they are tiny grains of sand. Add to that the slow deposit of bodily oils, suntan lotions and other chemical residue to the sand and you begin to round the shape of each grain thereby greatly lessening its effectiveness. Gummed up deposits are even more of a problem with products such as Baquacil™ (a biguanide based non-chlorine sanitizer which has a coagulating effect). Sticky deposits, excess calcium, and sand packs hard over time and may even lead to channeling. (Don’t worry you won’t need to enlist a mystic spirit medium to fix the problem!) Because of deposits and packed sand, channeling is simply water taking the path of least resistance around the outside of the sand bed along the edge of the tank and never really filtering through the sand (see Pic. 1). The result of all these problems is water that stays cloudier and less clean than it should be.
Picture 1 – BEFORE SAND CHANGE. Clear evidence of channeling is evident by the large gap between the sand and the left side of the tank. After about 8 years the sand in this filter shows clear signs of channeling, evidenced by the large gap between the left side of the tank and the sand bed. (see arrows).
Picture 2 – NEW SAND BED – After Sand change
Other effects of tired worn out sand are the need for more chemicals and longer filter run times as a result of debris not being effectively removed from the filter. For the cost of a few bags of sand and a little time invested, you could save yourself a chunk of change in power and chemical cost.
All these issues lead to the NEED to change your sand regularly. We recommend in ground pool sand filters be changed every 5-7 years, and above ground pool sand be changed every year. The reason for the discrepancy in time frame between in-ground and above ground filters has a lot to do with the power of the pump when backwashing is performed. Above ground pool pumps may be rated at the same horsepower as in-ground pumps, however the simple reality is that in-ground pumps have much more oomph (that’s a technical term) and erupt the sand bed in the filter when backwashing, doing a much more effective job cleaning the sand than any above ground pump can. Because of this, sand will last much longer on an in-ground filter.
So the next time you think sand is sand and don’t believe that it ever needs to be changed, think again. Your pool’s clarity and cleanliness could be at stake. In our next blog we’ll examine the best practices for changing out that old sand.