Couple Questions about Adding Diatomaceous Earth to Sand Filter

channing321

Member
May 23, 2017
11
Mesa, AZ
Hi all, just a couple of quick questions for those of you who add D.E. to your sand filters:

1. I know you have to add D.E. after you backwash because it flushes it all out. Do you add more D.E. every time you backwash? Or do you just add some after a heavy swimming load/rain storm, etc.?

2. Does the PSI increase of 1 also change when you backwash? You're supposed to backwash when the normal pressure goes up 25%. So if you sit at 15, you would backwash at ~18.75. With the PSI going up 1 with D.E. to 16, do I now backwash at 20, or do I stick with the original 18.75?

Thank you all in advance! After 3 years of pool ownership, I finally decided to listen to you guys and am in the process of SLAMing my pool right now. My water has never looked clearer or more beautiful than it does right now mid SLAM. I'm so excited to be able to maintain this thing looking so good all Summer.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
21,261
Laughlin, NV
1. You add enough to get a 1 psi rise in filter pressure.
2. Once you backwash your filter pressure should come back close to your normal clean filter pressure. There can be some variance in clean filter pressure. You always backwash once your filter rises by 25% over the clean filter pressure.
 

channing321

Member
May 23, 2017
11
Mesa, AZ
Thanks for the responses, mknauss. For my first question, I was more asking if pool owners who add D.E. to their sand filters add it every time after they backwash. I know if I want more D.E. in the sand filter that it must be added after a backwash, but should I add it every time I backwash? As in, is it beneficial to always have some in the sand filter or is it only beneficial to add it after a heavy swimming load, etc.?

As for question 2, that makes sense! Thank you!
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
21,261
Laughlin, NV
We have seen folks that add it after every backwash. Basically, they are making the filter 'dirty' at the start so it filters better. I would say try it without and see if the water clarity is sufficient for your liking.
 

channing321

Member
May 23, 2017
11
Mesa, AZ
This is the first time I've ever added it and the pool is looking very good. Granted, I've never SLAMed the pool either, so it could just be that. I'll hold off on it after the next backwash and see if I like how the water looks after a bit.
 

AUSpool

Bronze Supporter
LifeTime Supporter
TFP Guide
Sep 23, 2015
624
Brisbane, Australia.
Hi all, just a couple of quick questions for those of you who add D.E. to your sand filters:

1. I know you have to add D.E. after you backwash because it flushes it all out. Do you add more D.E. every time you backwash? Or do you just add some after a heavy swimming load/rain storm, etc.?

2. Does the PSI increase of 1 also change when you backwash? You're supposed to backwash when the normal pressure goes up 25%. So if you sit at 15, you would backwash at ~18.75. With the PSI going up 1 with D.E. to 16, do I now backwash at 20, or do I stick with the original 18.75?

Thank you all in advance! After 3 years of pool ownership, I finally decided to listen to you guys and am in the process of SLAMing my pool right now. My water has never looked clearer or more beautiful than it does right now mid SLAM. I'm so excited to be able to maintain this thing looking so good all Summer.
If your using DE you add it after every backwash, enough to raise your PSI by 1psi. Deciding when to use it is up to you, if you have a heavy swim load or a bad rain storm and the water looks ‘dirtier’ than normal than DE can help to improve your sand filters performance immediately after a backwash. If you are still SLAMing your pool and have the DE on hand I would continue to use it until you have finished the SLAM.

If your normal clean psi after a backwash is 15psi you backwash at clean psi+25% or 18.75psi wether you have DE in there or not. Sand filters operate at their worst when they are their cleanest - you’ve got to think backwards. As they get dirty or trap more dirt their efficiency improves. But the efficiency will continue to improve to the point of failure which is why we backwash at 25% of clean. Sand filters are least efficient when clean or immediately after a backwash. The DE adds 1psi of artificial dirt and increases the efficiency.

I know if I want more D.E. in the sand filter that it must be added after a backwash, but should I add it every time I backwash? As in, is it beneficial to always have some in the sand filter or is it only beneficial to add it after a heavy swimming load, etc.?
If your sand filter is working properly, normally and you are happy with the water clarity you shouldn’t need DE. If your water is dirtier than normal and/or if you are SLAMing and backwashing more than normal DE can help.

I use DE all the time but I think my sand filter with glass doesn’t work as good as it should. During winter when no one is in the pool I don’t bother with it.
 

jtpipkin

Bronze Supporter
Oct 2, 2016
153
albany, ga
Channing - I have a sand filter and use DE from time to time. I started using it to try and filter out the finer particles I could only see in front of the light at night. Think of it like 'polishing' your water. Nothing wrong if you use it from time to time or every time, but you will be backwashing more frequently if used every time. Throw in a filter sock and keep your water balanced and it will be hard to beat :)
 

channing321

Member
May 23, 2017
11
Mesa, AZ
Thank you all for the kind and helpful responses. I think I'll keep using it until my SLAM is done, and then hold off unless I'm not happy with the clarity of the water. Man, the water has never looked better during the SLAM and with the DE in the filter.