Dual Filters - Sand and Cartridge

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billy0952

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Apr 26, 2015
59
Leesburg, GA
I have a 20' Intex AGP that I'm in process of reopening. I have a Intex sand filter which came with the pool. I let the water turn green over the winter. Two days ago I started slamming. The green went away within a few hours resulting in the water turning grey. I scooped and vacuumed the muck off of the bottom. With the filter running 24/7 for two days now the water is still cloudy with visibility of maybe a foot or so deep. Wanting to speed things up a tad and after reading somewhere on here that a sand filter only filters particle sizes of 30 plus and cartridge filters get particle sizes down to 10 or thereabouts I came up with the hare-brained idea of trying a dual filter setup, sand and cartridge. I had an cartridge filter system from an older Intex pool. I ran the output of the sand filter to the input of the cartridge filter system and the output of that system back to the pool. I'm only running the pump on the sand filter system and it seems to handle pushing the water through the sand and through the cartridge filter and non-operating pump and back to the pool with no problem.

Has anyone else tried anything like this before? I figure the sand filter will catch most stuff and the cartridge will get the smaller stuff and not have to be cleaned out very often. Not sure I will continue this setup after the water clears up but who knows, I might? Any suggestions/recommendations? I have plenty of time right now due to little to no work as a result of the Corona virus.

Does anyone know if there's a relatively small cartridge filter available that hooks up separate from the Intex pump (or any other brand)?
 
ajw22 said:
Filtering does not fix an algae problem. You can put all the filters you can buy on the pool and you will not clear it until you follow the SLAM Process. With the SLAM Process your sand filter should be fine.

What test kit do you have? Pool Test Kits - Further Reading

When did you last backwash or clean your sand filter? Sand Filter Use and Care - Further Reading

I suggest you read ABCs of Pool Water Chemistry
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Thanks for the quick reply. I wasn't clear in what I was asking, my bad. I have a FAS-DPD test kit and have been slamming at a FC level of 14 with a CYA level of 30 now for about four days. The green went away within the first few hours but the grey cloudiness has lingered ever since with very slight improvement from day-to-day. The pool passed the overnight test last night and I've noticed a very slight improvement in clarity as visibility is now about 2' as opposed to 1' yesterday. I will of course continue the slam until the water is clear as that is a requirement in addition to passing the overnight test. I am disappointed that this is taking much longer than it has in previous years under very similar circumstances. However, I am confident the process will work as long as I continue the slam until the water is clear.

I've used a sand filter for the last several years and the water has sparkled and I've had no trouble maintaining it that way. My basic question is I was just wondering, in general, if there is any significant visible difference when using a cartridge filter which filters smaller particles as opposed to a sand filter which doesn't trap particles quite as small as the cartridge? (This assumes the water is clear and balanced to start with.) From reading an article on here is seems the only time I might notice a difference is night swimming with lights. As we don't swim at night I'm assuming I won't be able to tell a difference between just the sand filter and the sand/cartridge combo.

Note: I don't want to add anything to the sand filter.
 
billy0952 said:
I've used a sand filter for the last several years and the water has sparkled and I've had no trouble maintaining it that way. My basic question is I was just wondering, in general, if there is any significant visible difference when using a cartridge filter which filters smaller particles as opposed to a sand filter which doesn't trap particles quite as small as the cartridge? (This assumes the water is clear and balanced to start with.) From reading an article on here is seems the only time I might notice a difference is night swimming with lights. As we don't swim at night I'm assuming I won't be able to tell a difference between just the sand filter and the sand/cartridge combo.

Note: I don't want to add anything to the sand filter.
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The sand filter will be just fine. I truly believe that a sand filter is much easier than the other options, but that is just my opinion.

Now, I'm not sure why you wouldn't think of adding something. You just pour a little DE Powder (or in my case celulose fiber DE replacement) in the skimmer after you have backwashed. The powder settles over teh top of the sand bed and then filters the same small particles that other filters do. There is no opening the filter to "add" something to it.

The biggest problem people have with a sand filter is backwashing too often. It should only be backwashed when the pressure rises 25% above the clean pressure. Until then, the captured particles on the top of the sand bed act as a further filtering material. I always say, a dirty sand filter cleans better than a clean sand filter.
 
tim5055 said:
The sand filter will be just fine. I truly believe that a sand filter is much easier than the other options, but that is just my opinion.

Now, I'm not sure why you wouldn't think of adding something. You just pour a little DE Powder (or in my case celulose fiber DE replacement) in the skimmer after you have backwashed. The powder settles over teh top of the sand bed and then filters the same small particles that other filters do. There is no opening the filter to "add" something to it.

The biggest problem people have with a sand filter is backwashing too often. It should only be backwashed when the pressure rises 25% above the clean pressure. Until then, the captured particles on the top of the sand bed act as a further filtering material. I always say, a dirty sand filter cleans better than a clean sand filter.
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I'm probably guilty of backwashing my sand filter too often. I have it apart right now, flushing it out for its annual maintenance. While removing the valve on top the innards came up. As a result I've had to unscrew the "fingers" and remove the tube. Next I had to scoop out the sand so that I can center and reinstall the innards, using the alignment device that came with the unit. While working with it I noticed sand particles have blocked maybe a third of the openings in the fingers. I've cleaned most of that out and am in process of putting it all back together again and will reuse the same sand as it cleaned up nicely.

My pressure gauge does not have much resolution as far as reading PSI so to hopefully keep from backwashing too often in the future I'll probably just go by "feel" such as backwash when there is a noticeable drop in water pressure going back into the pool.

WRT adding the DE powder to the skimmer after a backwash, do you have to add a little more after the next backwash and each backwash thereafter if you want to maintain the extra filtering? Also, do you notice a significant improvement in water clarity after using the DE power as opposed to just the sand?
 
billy0952 said:
WRT adding the DE powder to the skimmer after a backwash, do you have to add a little more after the next backwash and each backwash thereafter if you want to maintain the extra filtering? Also, do you notice a significant improvement in water clarity after using the DE power as opposed to just the sand?
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Yes. Backwashing removes it and you need to add more.
 
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