Adding DE to a sand filter

[AnnaK]

I would like to learn what happens inside the sand filter when you add a small amount of DE.

Due to the leak in our pool it sat for 4 days without filtration. I added bleach and mixed it in manually but couldn't run the pump until the water level was high enough again. The dirt in the air settled on the bottom and billowed up in dingy clouds when I brushed. Having read about adding a small amount of DE to aid in filtration I did just that: I put less than 1/4 cup in the skimmer.

After about an hour the filter pressure had risen by 3 PSI. I was running the pump on low. After 3 hours or so there was no water coming out of the return though the pump was running and not particularly hot. I switched to the high setting and water flowed out the return again at what felt like its normal pressure. At the gauge, pressure had gone up by a total of 4 PSI now.

The pool was amazingly clean after running the water through the filter for 4 hours!

Am I correct in thinking that the DE layers itself over the laterals and incoming water is pushed through this DE layer into the sand? At low speed, is the pressure not high enough to push the water through the DE layer?

I backwashed yesterday and got rid of some very brown water but it cleared up much faster than it usually does. Pump clean pressure is back to normal (15 PSI on high) and the water is very clean.

[AnnaK]

Bumping this because I really am interested in how adding DE to a sand filter works inside the filter. Anyone?

[chrisexv6]

I dont think its making it down to the laterals.

Rather I think its filling the "gaps" between sand crystals, making the whole system "finer" in filtration. Ive read some people say its a coating along the top of the sand itself, that might be too (Ive never opened up my filter after adding DE to check)

Im with you though, all I know for sure is that it works I just backwashed my sand filter this morning so Ill need to add some more back in but the water does end up clearer. I think its a great middle ground between keeping the ease of use of a sand filter and getting DE-like (but not quite the exact same) filtration from it.

[AnnaK]

What really concerns me is that after a while no water was coming out of the returns when the pump was running on low speed. Something had become clogged after the DE was in for a few hours. High speed worked fine albeit at much higher PSI.

[BigDave]

Adding DE to a sand filter creates a very small DE filter by coating the top of the sand bed with DE. The usual recommendation for adding DE to help polish water in a sand filter is to add it 'til the pressure goes up 1psi - with 3psi rise, you had a denser DE layer that filled up quick.

With a centrifugal pump, the more water moved, the more load - less water, less load. The motor is cooled by the fan that blows over it. The pump is cooled by the water moving through it. I'd have some concern running a pump with zero flow that the water in the pump (no flow) would continue to heat up until it was too hot for the design of the pump components or it turned to steam either causing damage to the pump. I suspect that in your case (with the pump running on low and perhaps some flow) you're just fine.

[Watermom]

Dave,
Do you use DE in your filter and have looked to see how it looks after it is added or is this just the info you have read that Ben wrote elsewhere on the forum. Just curious.

[BigDave]

Nope, not personal experience. My answer is based on what I've read here and what I've observed. The sand bed looks (to me) finer than the material used in DE filter grids and fingers and this is the basis for my statement that the DE should coat the top of the sand bed. I would also expect DE to pass right through a sand filter's laterals based on my observation of my filter's laterals and the fineness (for lack of a more accurate term) of DE. So, some repetition and some reckoning - I hope I haven't misled.

I'm sure there's some penetration into the sand bed but I'd be surprised if the DE would be dispersed throughout. Increasing the pump speed and pressure probably did push the DE a little deeper, breaking up the layer that had formed at low speed.

I did use a cellulose DE replacement product last year that gave me no apparent performance boost. I discovered upon inspection at closing that it had clumped into what looked like a newspaper delivered to the driveway before a thunderstorm and driven over several times (this happens often in my driveway).

[AnnaK]

Thanks for the various explanations, guys.

[AnnaK]

Dave,
Do you use DE in your filter and have looked to see how it looks after it is added or is this just the info you have read that Ben wrote elsewhere on the forum. Just curious.

This begs for clarification. In order to offer an explanation or advice to the best of our knowledge, must we have personal experience with the issue? Or can we rely on knowledge we've gained from trusted, external sources combined with our own ability to analyze, internalize, and understand?

If I'm required to have personal experience with an issue before I attempt to help someone, I'm in trouble and I'd best just stay silent.

[Watermom]

Anna,
I was just curious if he had looked inside a sand filter that had used DE in it or not. I have not looked inside mine after I have added it. Just wondered if he had. That's all. Nothing more.