Pool Filter

Adding chemicals, vacuuming, backwashing,
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ttrulson

Pool Filter

Postby ttrulson » Mon 01 Dec, 2008 20:55

My husband is a very smart man, however when it comes to our pool filter, he falls down a bit. We had a sand filter until about 9 months ago for 15 years and the pool was perfect all of the time.

We had a leak, so replaced it with a cartridge filter system. he now says there is no reason to clean or soak the filters to clean them, as the more stuff that is stuck on the filter, the better it will filter.

Can you please help me to explain to him why that is faulty thinking. We are having issues with the pool now, and he is telling me it is my lotion, not the filter.

HELP!!


muss08
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Postby muss08 » Tue 02 Dec, 2008 23:39

You absolutely need to clean the cartridges in a cartridge filter! The fabric will get clogged, your flow will be greatly reduced and the pool wont get enough filtration. His line of thinking is TRUE for SAND filters because sand filters have larger gaps allowing larger particles through. So when smaller particles get trapped in the sand there is still room for water to pass through. Cartridge and DE filters catch much smaller particles so they clog up without letting much water past. To clean all you need to do is hose them down with a sprayer.
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pooldude
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Pool Filter

Postby pooldude » Sat 28 Feb, 2009 12:17

Cartridge filters are messy and yucky to clean. They may save us water and chemicals, but for ease of use nothing beats a sand filter with a multiport valve.
chem geek
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Pool Filter

Postby chem geek » Sat 28 Feb, 2009 13:46

Sand filters may be easy to backwash, but that uses more water. I live in an area where water restrictions are put in place so I have a cartridge filter. It's an oversized filter (4-cartridge 340 square feet total area for my 16,000 gallon pool) so I'm able to clean it only once a year (I also have an electric opaque safety cover that keeps the pool cleaner). That's the key to making cartridge filters easier to clean -- get an oversized filter and you don't have to clean it as often.

Richard
pooldude
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Pool Filter

Postby pooldude » Sat 28 Feb, 2009 15:03

Wow! Once a year!

I'm used to backwashing weekly in the summer, even when I don't need to. It's a habit I've gotten into. I vacuum then backwash. It also allows me to use trichlor without running into problems of excessive stabilizer buildup. But you certainly can't beat once a year.
chem geek
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Pool Filter

Postby chem geek » Sat 28 Feb, 2009 15:17

Yes, it's pretty amazing what a pool cover can do to help keep a pool clean, but also an oversized filter. There is no registered pressure increase on the filter during the year -- I can't even see 1 PSI increase. The filter is definitely dirty, however. It mostly has lots of cedar needles that happen to make it through the skimmer or pool pump baskets and has a layer of gummy flesh colored gunk in the deep fold parts of the filter that I suspect is mostly suntan lotion. In spite of this (or perhaps because of this), the water remains crystal clear so I know the filter is working. During the summer, my wife uses the pool almost every day for about an hour or so and on the weekends we have the pool open longer for several hours at least one if not both days.

I've also gone around 6 seasons without replacing the filter cartridges, but I plan on doing that this season since they do appear to be falling apart somewhat (at least the straps). Since there are 4 cartridges, this won't be cheap, but allocated over 6 years it's not that much. I've probably pushed them more than you are supposed to but as noted above the load on the filters may be lighter than is typical.

You are right that weekly backwashing means dilution, but keeping the CYA in check only happens to a great extent in smaller pools with shorter swim seasons. With Trichlor, for every 10 ppm Free Chlorine (FC) you also get 6 ppm CYA. So even with 1 ppm FC per day usage, that's 108 ppm CYA in 6 months. 7 ppm FC in one week would be 4.2 ppm CYA in that same week. If the CYA level were 50 ppm, then this requires a weekly 8.4% backwash (and splash-out, etc.) amount to keep the CYA level constant. So though backwashing certainly helps, it doesn't eliminate the CYA buildup. There are other factors that can lower CYA including a slow oxidation by chlorine itself, but this isn't a big effect though may be catalyzed (sped up) by iron in the water. Of course, in areas where there are summer rains, the water may get diluted from overflow and the same is true over the winter. Last, but not least, is when a pool is "let go" over the winter one can not only get algae, but soil bacteria can get into the pool and consume the CYA producing ammonia which upon spring opening looks like an insatiable chlorine demand.

Richard

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