Organic Matter In A Sand Filter?

[revitup]

A friend with an IG vinyl pool says that he solved a chlorine problem by changing the filter sand. His FC was depleting rapidly although there was no evidence of algae in the pool or other condition that was causing it. His theory is that there was organic matter trapped in the old filter sand that wasn't being removed by back flushing. The trapped organic matter was using up chlorine as the water was passing through the filter. Once he replaced the old sand with new the FC and CC levels normalized. Is this a likely scenario?

 

[Texas Splash]

Sure. While in theory you wouldn't think that algae would be able to grow without sunlight, we know it manages to thrive in dark areas like behind a light (niche), hollow steps, ladder rails, and as you described in the filter. In your friend's situation, it's very possible that a simple deep cleaning process would have sufficed as opposed to replacing the sand. Sand doesn't just go bad unless it was compromised with something sticky like floc or clarifier. But the sand can sometimes become firm/compacted or develop "channeling" where the water simply can't fall through the sand as designed. In any case, it sounds like what he did worked.

 

[duraleigh]

changing out the sand may temporarily fix the problem but it is a band aid. The conditions that lead to his clogged sand likely still exist and your friend will simply clog the filter again.

Chlorine is the answer. Adequate levels of chlorine kill organics (yes, in the filter, too). Backwashed correctly and deep cleaned every other year or so, the filter will never clog and there is no reason to ever replace sand.

 

[Donldson]

Algae is microscopic. So while cloudy water, small green patches, or constant brown sand-like deposits on the floor are some evidence of algae they are not the only ones. One major indicator is constantly depleting FC. Test results reveal more about what is going on in a pool than what is visible in the water.

His theory is very unlikely as organics in the filter would be quite minimal compared to those in the bulk of the pool water. If the chlorine level were adequate (we do not know his FC or CYA level, which would reveal much) then organics in the filter would be quickly eliminated. Chronic chlorine loss points to either low CYA or organics. As to changing the sand clearing up the issue, that is only his interpretation. A test result log would reveal a more likely cause, though testing itself could be the root problem depending on how reliable it is.

On a somewhat related note: this is why pool chemical reviews online are worthless. Your friend may have done a few things to the pool and the last thing he did was change the sand. Since it cleared up after changing the sand then he credits the sand change. However, it could have been any number of things. Same with any "miracle" pool chemical you find online. They are all full of 5-star ratings from people who think it cleared their pool because it was the last thing they did before it took a turn for the better. It's kind of a blind leading the blind situation and makes for some very odd (and sometimes awful) pool care advice.