troubleshooting RODI unit

[Spudsly]

I bought a used RODI unit, it's a spectrapure maxspec refurb unit with 4 stages plus an extra canister. I'm worried about the TDS coming out of the unit.

The water going into the unit measures 160-180 TDS with my handheld unit.

The first stage has one of the melt-blown filters. The TDS meter of water coming out of this stage reads ~200 on the in-line unit (somehow higher than what went in). The next stage is the carbon block filter and I believe the next stage is the same (though they do look different in the picture). Next the RO membrane and finally the DI resin. The water coming out of the unit reads between 4-10 on the inline unit.

I'm wondering how I should approach getting this lower. If it matters I have well water. We have a single stage unit on the water going into the house (just a simple pleated filter, which was absolutely horrifying when I changed it today). The PSI seems to be about 50 on the meter on the left (the one attached to the single stage) and when I check the waste:clean water ratio it seems to be roughly 4:1 (I didn't specifically measure it, I just put the outputs into two empty cups, but they had slanted sides so hard to say for sure).

Where should I start on this in troubleshooting the issue? I don't know much about the details of the actual filters that are in there... I thought that the seller told me the first and second stage had JUST been changed (like that day).

 

[mcgyvr]

sounds like the DI needs to be changed.. Water out of it should be zero..

 

[Spudsly]

sounds like the DI needs to be changed.. Water out of it should be zero..

I went and took a sample from right after the membrane and got 20 so I think you are right, DI is shot because what's coming out of it right now is ~10-15.

Although now I wonder if I shouldn't change the RO membrane since I've read I should expect 95% rejection and I'm only getting 90.

 

[Vinny Kreyling]

Well water CAN matter.
You have to check your water for CO2 since it can deplete your DI quickly.
Never had a well so I don't know the procedure but I'm sure you can do a search or someone will chime in.

 

[dyazdani]

First, I think your TDS coming out of the RO membrane is a little high and agree with the comments on changing the DI resin. You could consider adding a booster pump to make the membrane a bit more efficient. Your well's pressure tank runs on a range and so probably goes between 40 and 60 or so.

I have well water also in the 180 TDS range, my TDS out of the membrane was usually around 5-6 prior to having a pump. I added a booster pump and it dropped down to 2. CO2 can pose a problem in burning through resin, but I've been lucky.

 

[Spudsly]

First, I think your TDS coming out of the RO membrane is a little high and agree with the comments on changing the DI resin. You could consider adding a booster pump to make the membrane a bit more efficient. Your well's pressure tank runs on a range and so probably goes between 40 and 60 or so.

I have well water also in the 180 TDS range, my TDS out of the membrane was usually around 5-6 prior to having a pump. I added a booster pump and it dropped down to 2. CO2 can pose a problem in burning through resin, but I've been lucky.

Ok, interesting. Maybe I need to change the RO membrane too? I'll try the DI first. Does the refillable stuff work ok or should I be ordering the more expensive cartridges?

 

[Buckeye Hydro]

This might help - its from the FAQ's on the website:

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 more of the prefilters (all the filters that touch the water before it reaches the RO membrane) 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 much 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, goes 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 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 membrane 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 96% (i.e., they reject 96% of the dissolved solids in the feed water). So the purified water coming from your 100 gpd membrane would be about 16 ppm (a 96% reduction). Filmtec 75 gpd (and below) membranes produce purified water (a.k.a. “permeate”) more slowly, but have a higher rejection rate (96 to 99%). The lifespan of an 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 into 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 1 ppm, your resin needs to be replaced. Sometimes you'll hear people complain that their DI resin didn't last very long. Often the culprit is a malfunctioning RO membrane sending the DI resin high TDS 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

 

[2smokes]

If you have 5-10 after the DI cartridge you could think to change the resin or the whole DI cartridge.But you could do another experiment also.Let the water to flow slower through the RODI filter.Measure after 15 minutes of dripping at slower rate to see if there is a decrease in TDS.Sometimes if the wates has high pressure and high flow ,the DI resin doesnt have time to collect all the minerals in the water.