My system consists of a pre filter, 18 gpd membrane and a post filter along with two 3 gal tanks. I would usually get around 4 gal when filling jugs. Lately I’ve only been getting around 2 gal. I replaced both filters and the membrane and still only getting around 2 gallons after it sitting for hours, tank pressures are good. Any ideas on why it slowed down? After tanks are drained I’m only getting .5 oz/min which equals to 5.6 gal/day.

 

Your pressure tanks may need to be replaced. Turn off the water supply and completely drain the RO water (into containers so you can use it). Then pick up your storage/pressure tanks. If they are heavy or you hear sloshing when you shake them they need replacing. You may find it better to get one large tank instead of multiple smaller ones.

 

RO production is dependent on input pressure to the membrane; the lower the pressure, the lower the production. Is it possible your feed water pressure is lower than it used to be? Or if your system includes a booster pump, perhaps it needs to be rebuilt or replaced. I would check the pressure right before the membrane and see what the membrane specs say you should see for production at that pressure.

 

I drained the tanks and shook them, no sloshing. The incoming pressure is the same as it has always been, between 40-60 psi. I'm on a well and have had this system for years and it has worked fine up until a couple weeks ago. Even after sitting without use for 2 days I still only got about 2 gal. If I close off the tanks and leave the spigot open and measure how much water is going thru the system, I'm only getting .5 oz/ minute which is only 5.6gal/day.
This system is 30 yrs old, but I have rebuilt it and the only original parts are the filter housings. Maybe it's time to upgrade.

 

Take the filters and membrane out and see if you get full flow through the empty housings into the tanks. I'll bet something is plugged up somewhere.

 

When I started having problems I decided to change all the filters, they were due. I put it back together without filters and ran a bleach solution through it. After installing new filters the problem came back.

 

How heavy were the pressure tanks when you lifted them? If they are heavy they are likely water logged even if you didn't hear sloshing. If you didn't make a grunting sound when you picked them up then they may be OK.

Disconnect the tube from the filter system to the pressure tanks at the tank end. Put the tubing into a container. Turn the water on and notice how much water the system produces. If it is about the same as from the faucet then it's likely not the pressure tanks. If you get more water from the tube then you need to inspect the pressure tanks and also check between the tanks and faucet for a kinked line or partial clog.

Are you certain you used the correct replacement cartridges? If nothing else has worked I would remove the current filters and reassemble being very careful to make sure everything goes back properly. If a cartridge is improperly seated it could block flow.