RO/DI maintanance

[justme97]

Ok, my first ro/di filter (coralife) is about 8 months old and I have a few questions on maintanance.

1. Since they are more than 6 months old should I change the particulate and carbon pre-filters even though I've probably only produced a few hundred gallons?

2. How do I know if/when the DI cartridge needs to be replaced? The manual doesn't even touch on this...

3. For the membrane...the manual says it needs to be used once every 30 days minimum (or refridgerated) and there was maybe one or two times (before I really got my tank going) where I didn't use it for nearly 2 months and I didn't refridgerate it. Does this mean it might not be ok anymore and how would I know?


Thanks for any help...either way I think I'll order the pre-filters, they don't seem that expensive..

[gws76]

Do you have a TDS meter? They are a good indicator of when to change your filters or membrane.

I usually get 1 year out of my RO membrane, and about 9 months out of my particulate and carbon blocks. For the most part I use more DI resin than anything. When my TDS gets to 10 ppm that is when I change the DI resin. The resin is always a good place to start. In the end it just depends on what water quality you start with. There are other factors also. A good place to read about filter replacement and DI resin is air water ice. That site has answered a lot of questions.

[justme97]

No, no tds meter yet...just realizing I need one. Does that test the overall effectiveness of the filter or just a part of it?

[AZDesertRat]

A TDS meter does not tell you anything about the prefilter or carbon, it is strictly for tap water, RO only and RO/DI.
The prefilter traps suspended solids or big stuff and the carbon adsorbs chlorine so have very little to absolutely no effect of TDS.
Change your prefilter and carbon block at 6 month intervals regardless of how little or how much water you have made. At the same time disinfect the system using the vendors recommendations.

The membrane should last about 3 years if you keep up with the filter replacements and disinfection. DI is entirely dependent on how well your RO membrane works, if you have CO2 in your water and how much water you make. A TDS meter is your best friend here. I could not imagine owning a RO/DI system without a handheld TDS meter, I would be lost without it plus probably be adding bad water to my tanks since I would be blind. Color changing resins as we know them today are not very good indicators, I think this may change in the future but not today.

Always change DI resin when you first start to see anything other than 0 TDS or its too late. DI resin releases weakly ionized substances like nitrates, phosphates and silicates even before it is exhausted and you may not see them with a TDS meter so don't wait.

[gws76]

It test the total disolved solids your ro/di is letting pass by. So it tests the overall effectiveness of the ro/di. That is why I usually start with changing the di resin first. A cheap handheld one works well.

[justme97]

So the way it works is you first change the di resin if the tds readings are high.
How do you know if the membrane requires replacement? If new resin doesn't bring the tds readings down?

[AZDesertRat]

No. don't change the DI without first finding out how well the system if performing. Thats like throwing things at a problem but not solving the problem. If your RO membrane, which does 90-98% of the work, is not performing as it should you will blow through resin in no time and waste money that could have been spent on a new membrane instead.
Using a TDS meter, you first test your tap water TDS. next you test your RO only TDS before the DI and finally you test the final RO/DI water.
The RO only should be 95-98% less TDS than the tap water was to begin with, if not it may be time for a membrane. The RO/DI TDS shoul be 0 and change it when you first start to see anything other than 0 TDS consistently.

Just adding DI can get real expensive even if you buy in bulk. A membrane can soon pay for itself when you consider for every 2% you increase the RO membranes efficiency you double the life of the DI, a 4-6% increase in RO efficiency can save a mint on DI replacements. Test the water first.

[justme97]

Ok, thanks that makes a lot of sence...the di basically polishes the water.

Any suggestions on tds meters?

[gws76]

justme97,

Does your ro/di have just an RO outlet and then a RO/DI outlet? Listen to AZdesertRat, I'm having half thoughts today. He's right, first check just the RO side of your unit to see if the percentages are where they need to be.

[justme97]

Yeah, if I remove the ro tube from the di chamber than I can collect ro water...so once I get my tester I'll try that and evaluate how each part is doing to see if my membrane is still happy.

Ok...another question. For mantainance coralife instructs (http://www.marineandreef.com/v/vspfiles/pdf/CorRO3stnopump.pdf)me to switch the waste and ro output tubes comming out of the membrane and run it this way for 15 minutes to "flush" the membrane. But all this seems to do is direct waste water directly into the di chamber...I fail to see how this flushes the membrane...lol, any ideas??

[gws76]

I wouldn't run the waste line into the di chamber. It would just exhaust the di resin. I'm not sure on that question, my unit has an ro flush.

[justme97]

Perhaps the point of thier ro flush proceedure is just to switch the location of the flow limiter. If that is the reason then maybe I should simply disconnect the di chamber when performing this...