Sand Filter Not Clearing Green/Cloudy Water

by Ed

Sand Filter Not Clearing Green/Cloudy Water

by Ed Gotwals
(Lansdale Pa USA)

Ever since I put in a sand filter I have been having problems with green and or cloudy water. Are their diagnostics to determine if the filter is working correctly? I read that channels could be in the sand that would preclude or by pass the filtering effect of the sand. How do I check for this condition? How much sand should there be in the filter?

Thanks for the question Ed. You have green/cloudy water for a reason so I'd like to have your complete chemical readings: Chlorine, CYA (cyanuric acid/stabilizer), pH, Alkalinity, Calcium Hardness, and Metals (iron and copper) and names of any algaecides you may have used along with clarifiers, phosphate removers, and/or flocs. It makes troubleshooting much easier.

If you've recently installed the sand filter, within a couple of years and it doesn't see heavy use, then channeling probably isn't to blame. Channeling happens mostly with high-use pools and can with either residential or commercial. This is when there's a lot of oils introduced into the pool through lotions, make-up, sweat, etc...

This oil gets trapped in the sand and is similar to sandy lard. The water can't go through. Since water will always find the path of least resistance it will go around it, down the sides of the filter, and be returned back into the pool as unfiltered water.

You can simply remove the top of the filter and feel around the sides. If there is channeling you'll feel it. It's like a deep hole. There's an easy way to take care of this but I won't go through it until it's confirmed.

The amount of sand depends on the filter model. Let's take the Tagelus Sand Filter. The TA 40/TA 40D model uses 175 lbs. of sand and a 7¾ free board while the TA 50/TA 50D uses 225 lbs. of sand and a 9¼ free board. Check the side of the filter or your owner's manual for the specs.

Too fine of a grade of sand will clog too quickly. Most manufacturers generally recommend No. 20 grade silica sand. "Working correctly" is a very wide range. There's high, low, and no pressure, sand coming back into the pool, out of the backwash hose, no prime, short filter cycles between cleanings, filtration system improperly sized, etc... Each problem is separate.

Also, sand filters are not my first choice. That goes to cartridge filters. I found through personal experience that sand filters, like DE, can be a real pain.

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