When to change R/O Membrane, Carbon, and Micron Filters in Kent Marine Unit

[joshclovis]

I've had my Kent Marine RO TFC 24 GPD unit for about a year and have never changed any of the filters or membrane. I am starting to see some GHA in my tank. I also checked my TDS and it reads 6 ppm. What should I change? RO membrane? Carbon filter? Micron Filter? Or all three?

 

Thanks for any help you can provide!!

 

Josh

[megability]

I've had my RO/DI for almost 2 years without changing anything yet, still runs at 0, but it doesn't seem like 6 would be a cause of GHA, I think 6 is still considered extremely clean - maybe as clean as your water can get?

[AZDesertRat]

The carbon block and prefilter have NOTHING to do with final TDS and 0 TDS is NOT and indication of their condition.

You change the prefilter and carbon block every 6 months like clockwork regardless of how much or how little water you have made. These filters are there to protect the RO membrane which is the workhorse of the system and does remove TDS, 90 to 98% of it. the DI resin gets the remaining amount.

 

The prefilter and carbon block remove TSS or suspended solids, things say from 0.5 microns up to visible with the naked eye and of course adsorb chlorine. The RO membrane and DI resin remove TDS or dissolved solids, things in the 0.0001 micron range. TSS cannot be measured on a TDS meter since they are not dissolved.

 

You need three TDS numbers to know what needs changing for sure, but we know for sure you need a prefilter can carbon block without those readings since TDS will not tell you their condition.

To trouble shoot a RO/DI you need your tap water TDS, RO only TDS before DI and the final or RO/DI TDS. The first two will tell you your rejection rate or how well the RO membrane is working and the second will tell you how well the DI is working which in your case is terrible.

 

One problem with DI resin is it starts to release the contaminants it has captured even before it is exhausted and the weakly ionized substances go first and often do not register well on a hobbyist grade TDS meter. These include nitrates, phosphates and silicates so probably are the source of your problems. You should change the DI resin when you very first start seeing signs of anything other than 0 TDS. You should replace the RO membrane whan it is in the 94%-95% rejection rate or removal efficiency range since it starts eating DI resin much quicker ath that point. Keep in mind for every 2% you drop in efficiency you cut your DI resin line in HALF. It does not take long to pay for a new RO membrane at that rate.

[megability]

Great info AZDesertRat, thanks. I just checked and yea my TDS are certainly higher than normal and 0 now, so I guess I have some filters to order, should probably get a new RO and DI to be safe, and then plan on that 6month filter change schedule...