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Thread: waterflow of sand filter vs cartridge filter?

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    waterflow of sand filter vs cartridge filter?

    Hello all,

    I've got a question I'm hoping someone here will be able to help me with.

    I've got a 2 speed pump which I'd like to run at the lower speed in order to save on electricity. Unfortunately, I'm finding that it seems that I'm not getting very good water flow rate when using low speed.

    I've got a sand filter, and immediately after I do a backwash, the flow improves for a short time, but goes back to being poor within a few days. I've also noticed that if I set the filter to 'recirculate', the flow improves dramatically.

    I've read up on the procedure for performing a deep clean of the sand filter, but unfortunately, the way my filter is piped, I can't open it without cutting the pipes, so it's not something I've been able to try yet.

    If I were to replace the filter with a cartridge filter, would my water flow improve? I suppose I could have someone change the piping on the sand filter to make it easier to open it up and clean it, but I really prefer the idea of not having to do backwashes anymore.

    In general, which type of filter would allow for a higher flow rate at a low pump speed?

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    Mod Squad jblizzle's Avatar
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    Re: waterflow of sand filter vs cartridge filter?

    Welcome to TFP!!!

    So low flow is pretty much the whole reason to run on low speed, right?

    How does your water look? What is your filter pressure doing on high speed? We recommend a backwash when the pressure rises 20-25% over the clean pressure. If that is happening quickly, then your filter is doing its job.

    A large cartridge filter might raise the flow rate (and correspondingly use more electricity), but not if you have some kind of chemistry problem.
    Jason, TFP Moderator
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    Re: waterflow of sand filter vs cartridge filter?

    Thank you for the quick response!

    I guess I'm worried that the flow is too low. The skimmer doesn't seem to do a good job, and I'm worried that since the flow at the returns is so low, the water isn't being 'stirred' enough, and some parts of the pool aren't getting proper circulation.

    At high speed, the filter pressure seems to rise 20% within a week, which is part of the reason I think the filter may need a deep cleaning. I've never done it in the 3 years I've been living at this house, and doubt the previous owners ever did either.

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    Mod Squad jblizzle's Avatar
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    Re: waterflow of sand filter vs cartridge filter?

    Sounds like it is time for a sand inspection / cleaning.

    Again, what does your water look like? How do you maintain your chemistry?
    If you have algae, even if not visibly green, it can very quickly clog a filter.

    Please add your location (City, State or City, Country) to your profile and pool details to your signature as described HERE as it will help us help you.
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    Re: waterflow of sand filter vs cartridge filter?

    I've got a sand filter, and immediately after I do a backwash, the flow improves for a short time, but goes back to being poor within a few days.
    As jblizzle says, you have a problem with your pool chemistry - not the filter. Your filter is catching the organics that are living in your water and simply doing it's job. When it gets clogged from the junk in the pool, it naturally slows the flow.

    Proper chlorine levels and balanced water will eliminate that.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: waterflow of sand filter vs cartridge filter?

    I would really like to clean the filter, but like I mentioned, there's no way for me to open it up without cutting the pipes, and I'm not comfortable doing that.

    The water 'appears' to be clean. I use a chlorinator with stabilized chlorine pucks, and also add liquid chlorine every few days.

    - - - Updated - - -

    Quote Originally Posted by duraleigh View Post
    As jblizzle says, you have a problem with your pool chemistry - not the filter. Your filter is catching the organics that are living in your water and simply doing it's job. When it gets clogged from the junk in the pool, it naturally slows the flow.

    Proper chlorine levels and balanced water will eliminate that.
    I understand how chlorine can sanitize the pool, but it doesn't actually remove the organics does it? I mean the stuff is still physically there so wouldn't it still clog up the filter? Or does the chlorine actually break it down so it no longer gets trapped in the filter?

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    Mod Squad jblizzle's Avatar
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    Re: waterflow of sand filter vs cartridge filter?

    "Appears" clean? Could you read a coin on the bottom for heads/tails?

    The chlorine kills and can start to break it down, but the filter needs to remove it. The problem is if you do not have adequate FC (which is a function of your CYA level, see the FC/CYA Chart) the algae will reproduce faster than you can kill it and filter it out.

    How do you test your water?

    The fact that you use tablets concerns me as they build the CYA level up higher and higher and thus you need higher FC levels to be safe. But, since you are up north, you may actually get enough rain and water replacement for the winter to counter the rising CYA. Only test results from one of the Recommended Test Kits can give us a picture of what is going on.
    Jason, TFP Moderator
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    Re: waterflow of sand filter vs cartridge filter?

    Live algae in your pool flourishes often when you can't see it......but your filter catches it. Then more live algae grows (constantly) and your filter continues to catch it. The cycle never stops until your filter is clogged, slowing down the flow.

    When you have adequate chlorine in the pool, the live algae never grows and your filter never clogs.

    You must now kill the algae, filter out the dead algae and then keep adequate chlorine in your pool so the algae doesn't regrow - you must SLAM your pool.

    Please read "The ABC's of Pool Water Chemistry" up in Pool School to get you atarted.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: waterflow of sand filter vs cartridge filter?

    That makes perfect sense. Thank you guys for the advice. It seems like I've got a bit of studying to do.
    22k gal, IG Vinyl

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