Thanks Spruce.
Decided to go for the 4021 from daqua.
How much resin do you go through for polishing it off?
And how often do you change the 2 filters?
I have 20" prefilters and use a sediment and Fiberdyne carbon block filter. I get them from Gardiner.
I think Doug sells the 4021 with 10" prefilters and he has a Fiberdyne equivalent in stock.
The 20" Fiberdyne has a service life of 78,000 liters; waste and pure. Mine lasts me around 3 - 4 months. I have a water meter on my system so I know when to replace them.
The 10" Fiberdyne has a service life of 38,000 liters.
Now SeanK's experience with replacing the carbon filters is that he can get them to last longer and buys cheaper units and as far as he's concerned I'm wasting money buying more expensive carbon block prefilters and he makes a valid point. He argues that leaving the filters longer may reduce the life of the membrane but overall you will be saving money.
However, I don't know what the concentration of chlorine is in our water. According to Doug the further away from the dosing plant you are the less chlorine will be in your water.
The manufacturers will be building in a safety margin so for all I know, these filters could be good for the removal of more chlorine than the 78k. So I believe that sticking to the manufacturers recommendations is the best way forward for me.
Resin.
I have a 6.5 liter di vessel and on average replace the resin in it once a year. So a bag of resin will last 4 years although I did split a bag with another local windie last time as he was short of resin. My system is automatic. A float switch in the tank operates a normally close solenoid valve. When the tank is full the float switch cuts power to the solenoid valve and water to the r/o is switched off.
When the water starts again there is usually a tds spike in the output water of the r/o (tds creep). The best way to save resin is to redirect that initial r/o production phase until the r/o has settled down. Doing that will increase the life span of the resin. I don't bother. (My process is r/o, di and then storage tank. I pump pure water onto the van/vans.)
I have an inline tds meter so do periodically monitor the r/o performance. I have a sensor on the output of the r/o before the di and the seond one on the di output.