Filter Sizing

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fritz614

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Sep 13, 2011
95
Omaha, NE
I went and bought a new sand filter without looking up what I should have really gotten. I bought a 100# filter. With my previous filter and now with this one, I keep getting fine silt on bottom of pool. I assume it is coming from filter, since while I vacuum and the pump is on high, i see it slowly collecting again behind me. If I have my pump on low speed, accumulation is alot slower. I have a 2-speed 3/4 to 1Hp pump. Today, the pump had been on low speed and I kicked it up to high speed, and a cloud of dirt came out of return. There is brand new sand in filter too.
Am I just filling my filter up too quick and just need to backwash more ofter? Did I buy too small filter? My pressure never increased with all the silt in filter.... Pool is about 10,000 gallons
 
Filter sizing is usually just based on the pool volume. For your size pool, I would suggest a minimum of 18" diameter (larger being better) ... not sure how that equates to # of sand.

Which pump do you have? Add more info to your signature.
 
jblizzle said:
Across the widest part of the filter.

What model filter? Add that to your signature too.
Click to expand...

I was going to make fritz measure the circumference and divide by pi, but that works too. :mrgreen:

What type of sand did you fill the filter with? Brand and sizing? 16" filters are 100 pounds, 18" filters are about 150 pounds of sand while at 24" is about 300 pounds of sand.
 
Generally that would just mean more frequent cleanings. I would not think that your Dynamo would be able to blow the dust through the filter.

Did you backwash the sand to clean it before using it?
 

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Was it dirt, dead algae or sand that came out?

Sand could indicate a broken lateral.

Also, many sand filters have a problem with dead algae being too small to filter out so we usually recommend adding a little DE to the sand to filter that out, then backwash.
 
I have not checked my numbers in about 1 week, but when I opened it up from winter, all numbers were good. I did backwash new sand. I will have to recheck numbers and post again tomorrow, esp the OCLT. It makes a cloud when I brush it, too cold to get in and see if it is sand (temp is 60). Also, not sure if it means anything, but my pressure on the filter in only at 14psi when on high and 4psi when on low.
 
OCLT was 0

I figured out my problem, just not sure the "why's" of it. The same thing happened to me with my last filter, thought this new filter would take care of it. Thought of it last night and gave it a try and it worked.

For some reason, my return eye diverter needs to be left off when in high speed. Whatever physics or science is behind it, not sure. The pressure is backbuilding enough in the filter that it is allowing the fine silt to work its way thru??? Any physics gurus have any ideas?

I have a Doughboy pool and whatever size opening they have must be too small. Will have to measure it someday when the water is warmer.....

Thanks to everyone for their help and input with me!! I always love this site and have converted 2 people so far!!
 
As I said before, it could be dead algae. It is so small that on high speed it makes it's way through the filters.

Does the filter pressure go up when you move the eyeball? It could be that when you turn the eyeball, it slows flow enough so the debris doesn't make it through the filter.
 
That is the opposite of what I would expect. The lower pressure, which is expected, is due to the reduced head loss of removing the eyeball but that should result in higher flow rate and more dust being blown back into the pool, not less.

It could be that there still is dust being blown out but since you aren't pointing at the floor, it doesn't collect as quickly. Turn off the pump for a couple of hours and see if it settles out.
 
It could be a problem with the filter and under higher flow, it seals the gap while under low flow it allows the debris through. It might be worth while to take apart the filter to make sure you don't have any broken laterals or perhaps a broken multi-port.
 

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