Sand Filter not working correctly

DeanT2889 · Postby **DeanT2889** » Mon 22 Aug, 2011 20:39

30,000 gallon pool with sand filter. Sand was replaced recently. Filter vanes are intact. Spider Gasket is new. Spring in handle is new. We shock every week, but pool turns green anyway.

When we vacuum, it must be to WASTE, because vacuuming on Filter cycle puts algae back into pool. It's like the filter is being bypassed. If we shock, then floc, then vaccuum TO WASTE, we get a nice blue pool. But it only lasts a few days...then we're back to green.

It appears that the sand filter is getting bypassed....but why?

DeanT2889 · Postby **DeanT2889** » Mon 22 Aug, 2011 21:02

DeanT2889 wrote:It appears that the sand filter is getting bypassed....but why?

After reading other posts, I'm now wondering if this is a CYA problem? We've been operating for 3-1/2 years on 3" chlorine tablets without addressing CYA whatsoever. In fact, it's doubtful we've even tested the CYA level. Never had to...pool was always blue...till now.

Postby **Henry_R** » Thu 25 Aug, 2011 17:00

DeanT2889 wrote:
DeanT2889 wrote:It appears that the sand filter is getting bypassed....but why?

After reading other posts, I'm now wondering if this is a CYA problem? We've been operating for 3-1/2 years on 3" chlorine tablets without addressing CYA whatsoever. In fact, it's doubtful we've even tested the CYA level. Never had to...pool was always blue...till now.

That's a VERY safe bet. My HOA community pool was using trichlor and we had to drain twice to reduce the CYA level from well over 100 ppm.

A pool store can test your water, but you likely want your own test kit too since they can screw up the tests depending on how experienced the person doing the test is. And the CYA test you need done is a subjective test. Depending on the person viewing the test it can appear to be different. Even so it can get you in the ballpark to know how high the CYA is.

FAS-DPD test kits from www.tftestkit.net are what have been recommended to others at this forum.
Most kits give a only a 6-8oz of test reagent for CYA. Since the CYA test uses a lot of reagent per test you might get 4 tests out of them. This kit gives a bottle almost quart size which should get plenty more tests.

Postby **Henry_R** » Thu 25 Aug, 2011 17:05

DeanT2889 wrote:30,000 gallon pool with sand filter. Sand was replaced recently. Filter vanes are intact. Spider Gasket is new. Spring in handle is new. We shock every week, but pool turns green anyway.

When we vacuum, it must be to WASTE, because vacuuming on Filter cycle puts algae back into pool. It's like the filter is being bypassed. If we shock, then floc, then vaccuum TO WASTE, we get a nice blue pool. But it only lasts a few days...then we're back to green.

It appears that the sand filter is getting bypassed....but why?

Did you replace the sand yourself or have it done? Either way do you know what type of sand was used? The wrong type for your filter might cause it to filter improperly. It could still be the CYA is high as you suspected, but if the sand is an issue then you might have a two-fold problem.

DeanT2889 · Postby **DeanT2889** » Mon 05 Sep, 2011 21:27

It WAS the sand filter. I removed the waste line from the filter just to see what was going on. The valve was not sealing against the spyder gasket. Even though the spring was replaced on the filter valve, there was enough corrosion on the valve handle shaft, that the spring was not fully closing the valve.

The result: (1) Was losing water to waste during the filtration...(2) Water from pump/pool was bypassing the sand filter and flowing directly back into the pool.

Solution: Removed the valve cap with handle and spring. Took it back to the store and disassembled it. Replaced stem, replaced spring (again), polished internal bore, lubed everything, and reinstalled. No more leaks to waste, no more bypassing. Blue pool.