RODI Filter Lifespan

[thewbell]

I have a 5 stage RODI and I have to admit I have neglected it pretty bad. I purchased it in late 2013 when I started my 75 and it has been running ever since and providing all of my topoff and water change water. I make water in 30 gallon batches generally as I know that is the best for the DI resin. When I set up my 120 last month I checked the TDS for the first time since I got the filter and it still showed 0. My tap water is about 250 and I have checked both with my TDS meter (that I finally bought) and a friends. I have new filters for the unit but if I am still running 0 TDS is there any reason I should change them? I am not having any issues at all and have been holding 0 nitrate and phosphate in my 120 with 2 clowns, blenny, coral beauty, flame angel, watchman goby, cleaner shrimp, kole tang and foxface.

 

[reefwiser]

I check the operation of my Ro/DI unit each month. I test by checking the water going in to the unit with a handheld meter this makes sure the meter is working as TDS meter are notoriously defective especially those built into the units. I then check the out flow water should read 0 TDS. Every six months I change the filters just did that this week in fact.

 

[thewbell]

I have checked mine with two different handheld TDS meters because I figured there was no way I had 0 after over 2 years. The filters are going to be changed today regardless but this just seems odd to me.

 

[AZDesertRat]

Manufacturers recommend changing the sediment and carbon filters every 6 months. These two are there to protect the RO membrane and have very little to absolutely nothing to do with TDS. They protect the membrane from suspended solids, big stuff, and chlorine and need replacement when you start to see a drop in pressure on your inline pressure gauge and when you start seeing any evidence of chlorine in the finished water by using a simple, inexpensive low range chlorine test kit. Chlorine melts a TFC RO membrane at very low levels.
You use the TDS of your tap water and your RO only water to determine your RO membrane condition, which does 90-98% of the work and the final RO/DI TDS to determine your resin condition.
Most overlook the RO only TDS and this is the most important number since it is the workhorse and acts as pretreatment for the DI which only polishes it off.
The other important thing is to disinfect the entire system following manufacturers recommendations or using the method I have posted hundreds of times and a search will bring up at every filter change or at least annually.

 

[thewbell]

Thank you for the information. I read all the recommendations about changing filters but laziness got the best of me. I will be changing filters today (I bought all of the filters and membrane) and putting it on my calendar.

 

[AZDesertRat]

Make sure to disinfect the system while you have it down. Bacteria inside the housings and filters can be pretty ugly.

 

[thewbell]

I will be sure do disinfect as well. Thank you for your help as I probably would have just swapped filters and moved on.

 

[b4tn]

I was going to post something and saw this so will tag along. I hit the 7 month mark on my BRS 4 stage. I have a filter/Resin replacement kit on the way. My DI resin is almost all used up but I am still reading 0 TDS. Seems the general consensus is to replace filters every 6 months.

 

[AZDesertRat]

Every 6 months unless you are using high quality, low micon sediment and carbon block filters and you are monitoring headloss and chlorine breakthru.

 

[duckdodgers]

For some reason idk if my water is bad were i am but i have to change carbon and di filters more often then 6 months

 

[AZDesertRat]

Is it because of silt or particulates building up on them? Are you experiencing a drop in pressure on your inline pressure gauge?
With the proper sediment filter you should not have to change the carbon too even with silt. Many vendors use very coarse sediment filters which forces the carbon to trap what it misses when a better sediment filter protects the pores in the carbon where chlorine is adsorbed so a single carbon lasts as long as it should. Something interesting is you can see 40 microns with the unaided human eye so coarse filters like 5 or 10 microns aren't much better than a screen door.