Algae Going Back Into Pool

I have an above ground pool with a cartridge filter. I have shocked and treated the pool with algaecide.

The water just looks cloudy. But when I vacuum the algae is shooting back into the pool through the return. I have cleaned the cartridge and it does not seem to help. Any ideas?



Hi. What is coming through the filter is algae. Algae is made of small enough particles to blow right through sand and cartridge filters. It takes a combination of shock treatment, algaecide, and running the filter 24/7. Running the filter nonstop is the part most people do not do. Any time you have water problems let the filter run until the problem is gone.

Water problems are normally caused by not shocking the pool every two weeks during the hot months and not running the filter enough. The hotter it gets the more the filter needs to run. Some smaller units will only keep a pool clean if run twenty hours or more a day.

Comments for Algae Going Back Into Pool

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Jun 17, 2014
My Experience
by: Jason Charles

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Filter Problems

by Lee
(Indiana)

I change the sand in my filter every year (because I take the filter inside during the winter, it's just easier to empty out every year). This year the water flow from the pump is really strong and I cannot control the algae.

When I apply chemicals, it seems that the water isn't as clear even though I keep my pump on 24/7. When I vacuum the pool, the algae is blown back in even after I backwash. The pool is a 24 ft above ground pool.

I'm wondering if I didn't add enough sand to the filter when I changed the sand in May. Could this be why I can never get the pool cleaned and my water flow is really strong?

Any help would surely be appreciated.



Hi Lee. I would say the chances are very good your filter is fine. Mustard algae will blow right through a sand filter and go back into the pool. It takes a combination of running the filter 24/7, the right kind of algaecide and some vinyl shock treatment.

Having your water tested and reporting about the algae to the salesperson might get you hooked up with the right products to clear the water. Mustard Algae can be very tough to get rid of but until you do your water will not clear up all the way.

It is also a good idea to vacuum the pool every day in the waist position. Send the algae out the waist port, not back into the pool.

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Bugs Go By The Filter

by Steve
(Wisconsin)

When I vacuum bugs off the bottom of the pool I can see them coming back in through the return line. This happened late last season so I replaced the cartridge filter with a new one. Still same problem.

I have now gotten the bugs out with leaf net, but still a lot of brown dirt looking junk on bottom of pool even after many vacuum jobs.

I have a 1.5 HP Clearwater II cartridge filter system on a 24' round pool. I also have a diverter with solar panels. The system is so simple that I can't believe that anything gets back into the pool. Ideas??



Hi Steve. It is very true that algae will blow right through most filters. As for bugs, I have never heard of it, but I am sure the same principle applies. This page explains a little about the filtering capacities of the different types of filters.

Pool Filters

Everything under a certain size will go through the media in all of the different filter systems. This is certainly true with algae.

Sand filters have a vacuum to waist position that allows you to vacuum the pool with all the water going out the waist port. This means the water does not go through the cleaning media and does not go back into the pool.

This uses some water but is the best way to get rid of algae. A cartridge filter will probably not have this option. You may want to rig up a separate pump for the purpose of vacuuming the pool directly into the yard, not back into the pool.

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Bugs Go By The Filter

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May 23, 2014
murky water
by: Anonymous

When the water gets murky in my 12 X 24 pool because the sand filter won't remove the small dust and algae, I have found that alum works good to get the suspended particles to sink to the bottom of the pool.
I dissolve it in a bucket and shut off the filter and just broadcast the alum solution over the top of the pool and wait for it to settle overnight. I then siphon the settled alum & dirt & algae out of the pool out with a garden hose. I use the water to water the trees.
I found that using a garden hose doesn't waste as much water as using the pump, but it does take longer!

Has anyone found anything that can be added to the sand in the filter to help it remove these small suspended particles of dust and pollen?
I have tried a couple of things that are added thru the skimmer, but nothing seems to work.

There has to be some kind of floculant available that would make that small particles filterable with a sand filter. I just haven't found it yet! I fight this problem every year because I have a bunch of trees and hedges in close proximity to my pool.

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Vacuuming Algae

by Jessica
(New York)

We cannot seem to get our 27 foot round above ground pool clean. Every time we vacuum it, the dirty water comes back into the pool through the return.

Why is this happening? Someone told us to put algaecide in it to kill the algae but we did that and there still isn't a change. What else can we do?



Hi Jessica. Yes, algae will blow right through a filter and back into the pool. It will look like it was never vacuumed ten minutes after you did it.

Here are a few suggestions. The filter needs to run nonstop until the algae is gone. I would use a couple of doses of vinyl shock treatment and vacuum the pool as often as necessary. Always vacuum in the waist position. This will send the algae down the drain, or out into the yard, but not back into the pool.

This may take several days but it usually works. If not, have your water tested again, add more algaecide if needed but do not shut the filter off until the problem is solved.

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