Eventually smooth the rough edges of the individual sand gra

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onBalance

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Technical side conversation split off of this topic. JasonLion

I have been told by manufacturers of sand filters that sand "movement" and "agitation" especially during backwashing, will slowly and eventually smooth the rough edges of the individual sand grains causing them to lose some ability to filter out particulate matter. Whether that is absolutely true, I don't know. They also suggest that 5-7 years is the general recommended time to replace the sand. For what it is worth, manufacturers of sand filters don't necesasarily sell sand in the after market. I have experienced many water problems that are due to poor filtration, and at the very least, contributes to some water problems. Circulation and water flow is also another issue to consider.
 
Re: How do you know when to change the sand?

If that were the case, then the beaches of the world would be covered in dust or tiny balls. That sand has been shifting and moving and rolling over each other 24 hours a day 7 days a week for millions of years, and it's still sand

There are reasons to change the sand but it's not because it's a few years old.
 
Re: How do you know when to change the sand?

There are certainly a number of people around with ten to twenty year old sand who are not having any problems at all. There are also some nice micro-photographs of sand before and after use in the filter for years, which no visible change in the grain "sharpness" over that time.

The only common reason to need to replace sand is calcium scaling. If you get scaling in the filter you will need to replace the sand.
 
Re: How do you know when to change the sand?

I am not convinced that water doesn't eventually makes the sand smoother over time. Yes, sand still exists at beaches around the world, but there is very course sand, medium, and very fine sand at various beaches.
Also, we all know the river rock is smooth. Depending on the water flow (some streams in the west rarely flow with water, and some rocks to not get moved around very much and don't necessarily grind against each other, yet are smooth. We also don't know how large the rocks were originally and how much surface has been removed over the years. Yes, I know that rivers have been flowing for thousands of years, and my point is weak. But I am just saying. (Sorry for being argumentive). It is just that there are so many other sources that make the same claim.

I agree that sand may sometimes last 20 years or longer. But water flow velocity (motor size) through the sand can affect that time table, as does the times and duration of backwashing. One of my points is that if the sand does become smoother over time, even if it takes 20 years or longer, then that means that the sand is loosing some of its ability to filter some debris during and over that period of time. So some issues with water clarity can be due to that.

With my service routes, we usually have sludge and gunk issues that clog up the sand, not scale. Yes, we can usually clean that up, but sometimes it is too much work, so we just replace the sand.
Based on my experience, and for whatever reason, I think that sand loses filtering ability over time (just like other filters sometimes do), cleaning does not always work, and does seem the need to replace eventually. That is my main point.

Someone from TFP has probably alaready mentioned this in the past, but if the pool water isn't too cloudy, one can add two cups of DE or FibreClear to the skimmer and walk over the a return line and see if any cloudiness is seen coming out within a minute or two. This works with cartridge, sand, and even DE filters. Of course, one can also vacuum some dirt or algae on the bottom of the pool and also watch the return lines. If it does, then the clarity problem may not always be due to a lack of chlorine.
 
Re: Eventually smooth the rough edges of the individual sand

Certainly sand wears over time, it just happens so slowly that it is not going to affect your sand filter in any meaningful way. You will need to replace the entire filter long before there is enough wear on the sand to make any difference at all.

Sand does not filter by having "sharp points", sand filters by having very small gaps between the individual grains. Those gaps are actually smaller when the grains are closer to round. Sharp points would hold grains apart, leaving wider gaps between the grains and reduce the filtering efficiency.

Sand filters can degrade for a number of reasons. By far the most common reason is due to channelling. Sand filters that allow obvious debris from vacuuming right through the filter have become channeled (or far less often have something broken inside). Channeling is easily fixed without replacing the sand. Channeling is also much more common with larger pumps.

Re-setteling the sand bed, which is not commonly done, will remove any channeling that has developed and generally solves the problem. The process of re-setteling the sand will also reveal any more serious problems that might have developed, such as calcium scaling or the sludge/gunk family of issues (either of which can indeed force replacement of the sand). By the by, the sludge/gunk issues are actually extremely uncommon if your are following our recommendations for appropriate FC levels and recommended chemicals to use.

Adding DE to a cartridge filter is not a good idea. DE will typically become embedded in the cartridge fabric and permanently lower the flow rate. Using fiber products with cartridges, or either DE or fiber with sand, is fine.
 
Re: Eventually smooth the rough edges of the individual sand

Adding to Jason's comments, I see no reason to ever change the sand. What I do see as a good maintenance practice is to clean the sand thoroughly each swim season which few homeowners do.

Cleaning will remove most of any buildup of sludge, resettle the bed and generally, give your sand filter almost a completely new start. Checking the sand level, removing debris, sludge, etc. re-leveling the bed makes for a virtual new filter and would give the homeowner an indication of the health of his water based on how much stuff has been captured.
 
Re: Eventually smooth the rough edges of the individual sand

Jason and Dave, I agree with most of your points. Channeling is definitely a major issue, and that breaking up the sand by stirring and re-settling generally works to clean and restore the ability of the sand to filter properly. And that DE is not suitable for cartridge filters. My service company began using 2 cups of FiberClear (instead of DE) more than 10 years ago for clarity problems with sand and cartridge filters, and I had forgotten that that was one reason for doing so. Ninety percent of our service routes are "chemical only" where we are not responsible for the cleaning of filters and vacuuming of the pool. So we end up with some filters not being maintained and cleaned properly by the pool owner, or not running enough hours, and so forth.

Only about 15-20 percent of our pools on service have sand filters, yet 90 percent of our water clarity problems are with sand filters. And we maintain our chlorine levels much higher than normal. Perhaps you can understand why I question sand filters and their durability and longevity, especially since the sand filter manufacturers tell me that the sand eventually wears out. But perhaps it has more to do with not being able to get the sand "clean" at some point in time.
 
Re: Eventually smooth the rough edges of the individual sand

I'll see if I can Get Brice Johnson to comment on this....he's a filter engineer with pentair and his input will be interesting.
 
Re: Eventually smooth the rough edges of the individual sand

This topic also came up in this thread where I wrote this post with references that seem to indicate that sand does not wear out physically in the lifetime of filters. Now that isn't the same thing as saying that sand doesn't lose its filtration capability. That can happen from other factors such as Jason mentioned. Biofilms can form which cause channeling. In fact, anything chemical that "sticks" to the sand causing it to clump would be a problem and if such things don't get backwashed, then only a thorough "cleaning" of the sand removing such materials would restore the sand to its original performance level. I'm speculating here.
 
Re: How do you know when to change the sand?

"The only common reason to need to replace sand is calcium scaling. If you get scaling in the filter you will need to replace the sand.[/QUOTE]

To JasonLion:

I don't know if this is part of the topic, however I have calcium scaling in my fiberglass pool for almost a year, try to fix it without not result yet. I have a sand filter, so that means to me, I don't have a good result because I didn't change the sand in the filter? Maybe I misunderstood or confuse, can you explain a little more on this for me please...

Thank you.
 

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I was specifically talking about sailing inside the filter, so the sand turns to rock. Scaling in the pool is unrelated to my comment (though pool scaling might happen at the same time as scaling in the filter).
 
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