I have some experience with diesel engine filtration system, where the final stage will remove about 2 microns. Its part of my work that I attend to these engines and its system.
When I started to want to know about my pool filter system, I can't find any manufacturer data on their filter nominal filtration rate. I know there is no such thing as 100% filtration. Usually its 98% or around there. Some filters even specify Beta Ratio.
I understand that water clarity when the chemical & sanitizing balance is good, its all about filtration and filtration means water circulation in a pool. Water circulation also broadcast the sanitizer well.
I read that sand filter is anything from 60 to a 100 micron. This is why I am not happy at all with sand and installed a cartridge filter downstream the sand, knowing that cartridge filter is about 10-20 micron rating ( so they claimed ). The other reason for using this cartridge is because when vacuuming, I do not need to throw water...I can trap fine dirt with cartridge filter, but not the sand. So I am saving money on water actually and getting clearer water at the same time.
I have wanted to use DE but since it has more maintenance, instead I chose natural volcanic Zeolite to replaced my sand, the brand is Zelbrite and the colour is red. While using Zeolite/Zelbrite, I realized that the 3-5 micron rating is probably not true, even though if it is true.... the way the sand filter works, the gaps between the zeolite will allow particles bigger than 3 microns to pass thru. So I suppose sand filter by its design ( stacking of sand grains ) has very low nonimal filtration rate...how much ...I don't know. All I know that my cartridge filter still get dirty ( but much slower though ) while being downstream of what is supposed to do a 3-5 micron rating.
The result of using Zelbrite is good. I backwash much less. Water clarity is better than sand + cartridge. The Zelbrite is the last addition I made. The Zelbrite does all it said it will do fairly well, its just I am not able to define nominal filtration rate for sand filter replaced by Zelbrite media and for the cartridge.
I use torchlight at night to test for suspended particles in my water, sort of turbidity test.
If there is a cartridge filter if anyone knows, that can do 5 micron filtration, I would like to get one.
I believe that for maximum clarity/visibility I must remove smaller particles that my cartridge can't.
The pool is for dive training, so I realy like to see maximum water clarity. I am quite paranoid when my pool do not have sparkling water. All the divers wear mask, so they can immediately see if end to end at 36 feet of the pool is not clearly visible, then water is not good. I have very clear water and above average, but I am trying to get even better clarity if possible.
Is it adviseable if I now install a DE downstream of my cartridge ? I am guessing that the DE will get clogged very slowly since there are 2 filters already upstream.
When only sand was used, clean filter pressure was 5psi. When cartridge was added, the sand filter starts at 10 psi clean.
The cartridge starts at 3-5 psi clean.
Ted sticky on DE stated 8-20 psi clean filter pressure, assuming the worst at 20 psi and I buy a very big DE filter to reduce head loss, is it right if I calculate 10psi clean sand pressure will be raised to 30 psi worst case ?? If I start at 30 psi clean on the sand, that means 40 psi dirty and the sand filter housing is rated I think 50 psi....borderline.
What are the typical clean pressure reading of DE for in ground pool and pump 3 feet above water line ?
What is your advice on this DE addition guys ?
Many thanks in advance.