Backyard Swimming Pool Sand Filter

by Robyn

It has looked like I have sand in the bottom of my pool. The pool shop people have been around to check the laterals and they are fine (they removed the sand in the pump twice & put it back together without a solution) but it keeps on happening.

When I put on the pool pump the particles are formed and become lumps (that sure look like sand) all over the bottom of the pool. They have now just spoken to a person this guy trusts and he now informs me that the problem is that I have bought a cheap 'pool chlorine' and the 'calcium hypochlorite' has built up over time.

What looks like sand is the calcium hypochlorite particles formed and become lumps (that sure look like sand) all over the bottom of the pool.(feb - to Oct 2011)I have also been told that if it was sand it would only come out of the jet stream in that area not all over the pool as it does.(We just bought this house and the previous owner used the capsules for chlorine.)

We had the pump moved from one place to another and it was after this that the 'sand'? started happening because the guy that moved it put new sand in. After that it happened and it looks like sand so I didn't imagine it to be anything else. The guy at the pool shop said.. I am to vacuum it up while on waste then fill pool up and vacuum again on waste and continue this way until it all goes away.

Have you heard of this build up before??? Any answer from you would be most welcome.

Thank you


Thanks for the question Robyn

I've never heard of something that looks like sand settling on the bottom of the pool when you use calcium hypochorite. When cal. hypo. is used, especially after shocking a pool, the calcium does settle to the bottom, but when brushed, it forms a cloud. It's not gritty like sand is. Cal.hypo. can cause cloudiness, but to
the best of my knowledge, not build up of calcium in the filter. If it did this would cause the filter pressure to rise.

I would first ask what is your calcium level? It should be between 150 - 250ppm. If you have hard fill water, you should stop using granular chlorine and switch to liquid. The pool doesn't need any more hardness.

Next is to check your total dissolved solids. This should be no higher than 1500ppm. If it is, or the calcium hardness is above 300ppm, a partial or full drain and refill is needed.

Let's say those numbers are in order. We need to look at the kind of sand being used. Most sand filters can use #20 silica sand. Be sure you're using the right size for your filter.

You've checked the laterals and said they're alright. Here's a list to look over and some troubleshooting tips:

Is sand returning through the returns after back washing? You need to RINSE after back washing.

Is the sand greased up? You may have channeling.

1. Broken lateral and/or diffuser

2. Channeling

3. New sand

4. Old sand

5. Not doing the RINSE after backwashing

6. Not checking the "freeboard". This is the measurement in inches from the top of the sand to the top of the filter. check with your sand filter manufacturer for this measurement.

Check the Multiport valve as well.

The spider gasket may have gone bad or is crusted up or the compression plate and compression spring might be going bad.

As you can see there are many pool owners that are having the same issue. The links above can help.

If you have new sand, there will be a settling in period. New sand is full of dirt and small particles that will get returned back into the pool. There's simply no way around this. The good part is it should only last about 1 - 2 weeks before the sand settles into the filter. At this time you should check the freeboard and top off the sand if needed.


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