RODI Filter and Media Changes

[+Grog]

How often do you change yours?

Do you use the TDS meter to tell you when? Or do you just change after so many months? Or do you go by the color of the DI media?

I can see my DI media changing colors but my TDS is still 0 on the out side and still ~13 on this in side, so I'm not concerned, just wondering what prompts other to know 'it is time'.

Grog

[+Capt. Obvious]

meter, although I have color change media...and 13 on the inside is amazing...i am guessing you have a water softener...mine comes in at the mid to high 200's leaves at 0

[+Capt. Obvious]

wait you mean IN to the DI...not IN to the entire filter....sorry

[+Grog]

Yes, I'm measuring into the DI and out of DI, not the in to the raw side. Last I had that checked was via Ward labs, it was 357 TDS out of the tap! (Had a full analysis done for my brewing....)

So the RODI is rocking! 357 to 0

[victoly]

I go by a) time (mechanical quarterly, carbon semiannually, DI annually, RO every two years), b) quantity (just estimated) and c) filter color on the prefilter and DI resin. I'm switching up my carbon styles here to deal with chloramines, I'll keep everyone updated.

[Richard L]

Meter for me. I don't know what my water is going into the system but its usually 4-6 into the DI and 0 out. I've been paying the two dollars extra for the color changing but I found that there isn't an obvious color change when the meter is reading 1-2 TDS coming out so I think I'll switch to the regular and pocket the dinero.

[+Capt. Obvious]

I have 5 lbs of the color changing media so *shrug* I guess next time I'll save the $

[Bpb]

Spectrapure csdi60. Bought used. Put new 0.5 micron carbon block and sediment filters. New di resin. Change carbon block and sediment filter every 6 months. Was gonna use my tds meter to tell me when to change the membrane and di.

It's weird but my tds is calibrated and working. Tap water tds is 553. RO stage takes it down to 1-2ppm, di takes it to 0. Checked into the filter being TOO efficient but apparently that's not unheard of for this particular unit. Pressure is at 75 psi and have a 4:1 rejection

[Buckeye Field Supply]

A good rule of thumb is to replace your sediment filter and carbon block after six months. A more precise way to maximize the usable life of these two filters is to use a pressure gauge to identify when pressure reaching the membrane starts to
decline. This is your indication one or both of the filters is beginning to clog.

Also be cognizant of the chlorine capacity of the carbon block. A good 0.5 micron carbon block for example will
remove 99% of the chlorine from 20,000 gallons of tap water presented at 1 gpm. Some original equipment suppliers commonly provide carbon cartridges rated at 2,000 to 6,000 gallons. Remember that all the water you process, both waste
water and purified water, go through the carbon block.

Regarding your RO membrane and DI resin, use your total dissolved solids (TDS) meter to measure, record, and track the TDS (expressed in parts per million [ppm]) in three places: 1) tap water, 2) after the RO but before the DI, and 3) after the DI.

The TDS in your tap water will likely range from about 50 ppm to upwards of 1000 ppm. Common readings are 100 to 400
ppm. So for sake of discussion, let's say your tap water reads 400 ppm. That means that for every million parts of water, you have 400 parts of dissolved solids. How do we go about getting that TDS reading down to somewhere near zero?

If you do some experimenting with your TDS meter, you'll note that your sediment filter and carbon block (collectively called “prefilters” because the treat the water before it reaches the membrane) do very little to remove dissolved solids. So with your tap water at 400 ppm, you can measure the water at the “in” port on your RO housing and you'll see it is still approximately 400 ppm.

The RO membrane is really the workhorse of the system. It removes most of the TDS, some membranes to a greater extent than others. For instance, 100 gpd Filmtec membranes have a rejection rate of 90% (i.e., they reject 90% of the dissolved solids in the feed water). So the purified water coming from your 100 gpd membrane would be about 40 ppm (a 90% reduction). Filmtec 75 gpd (and below) membranes produce purified water (a.k.a. “permeate”) more slowly, but have a higher rejection rate (96 to 98%).
The lifespan of a RO membrane is dependent upon how much water you run through it, and how dirty the water is. Membranes can function well for a year, two years, or more. To test the membrane, measure the TDS in the water coming in to the membrane, and in the purified water (permeate) produced by the membrane. Compare that to the membrane’s advertised rejection rate, and to the same reading you recorded when the membrane was new. Membranes also commonly produce purified water more slowly as their function declines.

After the RO membrane, water will flow to your DI housing. DI resin in good condition will reduce the TDS in the RO water down to 0 or 1 ppm. When the DI output starts creeping up from 0 or 1ppm, you know that your resin needs to be replaced. Sometimes people complain that their DI resin didn't last very long. Often the culprit is a malfunctioning RO membrane sending the DI resin “dirty” water. This will exhaust the resin quicker than would otherwise have been the case. Sometimes the problem is poor quality resin – remember that all resins are not created equal.

Additionally, don’t forget to sanitize the entire system at least once per year, and wash and lube your housing o-rings with food-grade silicone grease every filter change.

Russ

[Bpb]

That last part is interesting. I bought my unit used about a year ago and I don't know that it was ever cleaned. May have to look into that