The illustration to the left shows the comparative sizes of material each of the three filters available to us, (Sand, Cartridge and Diatomateous Earth) is capable of removing from pool water.
To give these circles some perspective, end-on, a slice of human hair would cover the entire illustration box.
Until Janssen invented the microscope, we assumed a Sand filter (the original pool filter) was catching all the bad stuff.
DE powder is the only filter capable of taking out bits as small as 6 microns, even capable of nabbing Cryptosporidium parvum virus and the terrifying flesh eating bacteria and why the vast majority of commercial pools use the open tank Vacuum DE system to filter their pools.
That's when everything is working properly. And when it's not, the open tank system makes it easy to spot the problem
Basically, the recirculation pump pulls water (the vacuum action) from a filter tank. This water is pulled through filter grids wrapped in fiberglass cloth. This cloth holds back any visible material in the tank including DE powder, leaves and other debris. As the water level in the tank drops, more water rushes in from the pool through main drain and gutter pipes.
It's the DE powder that catches all the smaller stuff. Even pool people find it hard to grasp that the powder is the actual filter. Everything else you see is just there to keep the powder in its place.
Under a microscope, DE flakes resemble a screen door. Pull water through these flakes and any impurities get caught in the screening. When the screening becomes clogged enough to slow the water flow, you can either rinse or backwash the filter.
Understand that DE powder is pulled into place when the pump is turned on and held in place until the pump is turned off. Dirt and other debris is brought in constantly from the pool and eventually forms a coating over the DE. When this coating becomes thick enough, the flow drops.
When a residential pump shuts off at the end of its daily cycle, all the material held on the grids falls away and settles to the bottom of the filter canister. The next day the pump clicks on again, everything in the canister is stirred up and you start with an almost brand new filter. In fact, the best residential filter ever made was the Sta-Rite stainless steel 'spin' filter that allowed the homeowner to spin the grids to shake up the DE powder.This process is also known as rinsing.
Because commercial filters generally run 24 hours a day, the pump must be turned off manually to allow this debris to fall away from the grids.
It takes about 5 minutes to rinse an open DE filter. Simply close the main drain and gutter valves and allow the pump to draw water level in the tank down to the middle of the grids, or until the pump loses its prime. Shut off the pump and use a garden hose fitted with a turbo nozzle to effectively spray everything off the grids. Add a scoop or two of fresh DE powder, open the main drain and gutter valves to get everyting in the tank stirred up. When the tank is refilled, turn on the recirculation pump. You'll have a filter that's almost as good as new and should, even during the swim season, last another week or two. You can generally rinse a filter up to half a dozen times before you'll have to do a complete backwash.
The enemy of every pool filter is sun tan oil.
To rid an open DE system of oil, perform a standard backwash cleaning of the grids, closing the main drain and gutter valves, drawing the water down as far as you can with the recirculation pump and hose the grids clean. Use your hose to keep all material in solution and draw the rest of the water out of the tank with the maintenance pump.
Add a healthy squirt of a good grease cutting dish soap (Dawn, Joy or Dove) and 1 gallon of acid to 1 gallon of water in a 2.5 gallon plastic sprinkler can. Sprinkle this mixture over the grids and move away from the tank while the acid goes to work. In about 15 minutes, open the main drain valve until the water level touches the bottom of the grids. Rinse the grids with a garden hose. Use the maintenance pump to discard this water. When the tank is empty, turn off the maintenance pump, add the appropriate amount of filter powder, open the main drain and gutter valves and when the water level in the tank stops rising, turn the recirculation pump on.
You'll have a fresh, as good as new, filter.
Our Pool School PRO CD contains hundreds of tips to save you money with Pool Maintenance, Renovation, Leak Repair and Construction.
Check out the Articles below for Great Free Tips!
Buy Pool School | Archives | Help | Praise | Links | Great American Pools, Inc
Excerpts from Pool School, pictures, text, graphics and web page design © 1997-2016, Scott Cruikshank, all rights reserved. Reproduction in whole or in part in any form or medium without express written permission of the author is prohibited.