I’ve had a couple of questions about the final filter bags I use in my pool so thought I would post a description and some pictures.
The bags are made using a heavy felt bag from MacMaster-Carr. They come is pore sizes from 1 micron to 200 microns. They are held in place with adapters that screwed into pool returns. The bags I use have a 1 micron rating and are 7” dia X 32” long. They are rated for a flow of 220 gpm and 50 psig. In my experience they need to be replaced about every two years for maximum filtration efficiency. After that the effective pore size seems to enlarge to something like 25+ microns. The bags come with a plastic flange in the top that needs to be cut off.
One of the best uses for the bags is in clearing up an algae bloom. During the normal shocking procedure the water starts out a nice forest green color. As chlorine begins to work the green color starts to fade and dead algae starts appearing on the bottom of the pool. The green color slowly disappears and the pool turns a cloudy white with dead brown algae deposits in front of the returns. The pool will finally clear up and I usually had to vacuum the dead algae to waste.
With the bags in place the pool goes from a nice deep green color, to lighter green, to clear with a slight green tint, to crystal clear, there is no dead algae deposit on the bottom, and it never turns a cloudy white. The bags remove all the dead algae and the white stuff that usually forms. My shocking time from green swamp to clear pool went from two or three weeks to three or four days. They are also very effective at making an almost clear pool look like clean glass if you have a sand filter. I believe you will be surprised at how much stuff gets though the sand filter and is picked up by the bags.
There are a couple of cautions when using the bags to help the pool clear up. One is you cannot just install the bags and forget them. They need to be monitored and checked for plugging about twice a day. If they fill with dead algae and debris they can almost shut off the flow of the pump, or they may break. They are easy to clean just by removing them from the adapter and hosing them down with a water hose. They can be turned inside out and hosed off or if they are real dirty just put them in the washing machine with lots of hot water, soap, and bleach. I usually turn them inside out put them over a broom handle and hose them down.
The adapters are made from three parts – 1.5” PVC screwed adapter, 1.5” pipe cap, and about 3” of 1.5” schedule 40 PVC pipe. The pipe cap needs to have a ½” hole drilled in the middle. This is to prevent the pump from running off the curve which can cause the motor to overheat and trip out. I’ve attached pictures of the adapter and bags below.
MacMaster-Carr link: http://www.mcmaster.com/#standard-filter-bags/=sri12c The MacMaster stock number is 5162K116