RO/DI questions.

[the other tang]

I have a 4 yr old RO system that I recently added a Spectrapure Maxcap dual stage DI to. It has the dual TDS sensors for in and out measurements. These were showing low at start up and then quickly went to zero, until last week. Now I am getting 180ppm in and out it claims. OK, the 1 micron sed filter is 1 wk old, carbon is 5 wks old, membrane 5 wks, DI 3 wks. I think I am seeing a false reading, every component of the system is either new or too new to show these readings. Grasping here but I need to figure this out. My sed filter fills up with iron deposits in approx. 150-20g or 4-6 weeks. Is it possible that could somehow cause these #'s? It doesn't seem likely because it would screw up the membrane, or is that the problem. As you can see I am chasing my tail here. Please Randy, AZdesertRat HELP!!!!!!

[Randy Holmes-Farley]

The measurement is before and after the first DI? Or the second?

Couldn't the DI just be depleted?

[the other tang]

They are between the first and second DI and after the second. Is is possible to depleat a DI filter in 1 month, I am only making 10-20g per week. How reliable are these tds meters? I fogot who makes them but are standard issue from Spectrapure.

[Randy Holmes-Farley]

TDS meters are normally reliable, but that does seem pretty fast to deplete (unless the RO is shot). Do you know the TDS of the tap water? You might remove the DI resins and pass tap water and post RO water through the meters and see what you get.

You might also ask in the Spectrapure forum here at RC to see if they have any suggestions.

[AZDesertRat]

First try reversing the probes and see if you still get the same readings. Do you have access to a handheld TDS meter to confirm the readings?
I suspect the meter is bad but your membrane may also not be seated properly and you are bypassing the RO all together. It happens sometimes. I also have a full MaxCap RO/DI system with two of the inlines but I still rely on the handheld meter for accuracy.

[the other tang]

AZ, do membranes come unseated from time to time? I put a new one in weeks back and got 0 tds then something changed, and I started getting high #'s. I don't have a hand held tds meter, and am new in LA so that might be tough to come up with. I sent this same Q to spectrapure via email a few days ago but recieved no answer. Do you see different readings from your inline and handheld?

[AZDesertRat]

Normally once a membrane is installed it will not move. It is possible for a housing to develop a hairline crack though or an o-ring to roll over or fail.
Yes I do see different readings between the handheld and inline meters. The inlines are not temperature compensated in that they have an external probe that reads air temperature and not water temperature so if they are not exactly the same the readings are off significantly. Recently I posted a link to a graph showing temperature corrections factors and it can be off quite a bit. I do know Spectrapure is working on a new water quality monitor probe that is truly temperature compensated with an internal processor with look up tables that should be very accurate. I saw the working prototype so it should be available soon.

[the other tang]

OK thanks. If the unit was calibrated at x temp, and I am using it a y temp then I can understand why it would be off. Is there a way of finding what X is? I do not heat the laundry room where my RO/DI is and it is probably 60 degrees in there all 4 weeks of winter here, do you have a correction chart? You siad you do see a dif reading from the tds meters, does that mean the inlines are inaccurate or just less accurate than your handheld?

Also how are the pleated filters working?

[AZDesertRat]

The problem with temperature and conductivity is that it is not linear so its not easy to calculate. It requires math calculations and thats where the electronics and look up tables come in. Here is a small article I borrowed that sort of explains it.
http://www.eutechinst.com/techtips/tech-tips44.htm

I have not installed the new 0.2 micron pleated filter yet, I pick up my water meter early next week and want to get it plumbed in first so I can start recording total gallons passed through the filter array.

[the other tang]

Since this is my thread I guess I have the right to get off subject.

I have thought about that several times, I a very familliar with vrious types of flowmeters. What brand and type/design are you getting? Is the counter resetable, or do you rely on a log for changes and such.

Off subject again. Have you or anyone else tried pressure gauges to show pressure differentials before and after filters for changes? A sediment filter might be the place for this rather than DI's. I was thinking there might be a differance between dirty to the eye and a loss of flow due to a restricted fliter being full.

[AZDesertRat]

The flowmeter I am installing is a standard residential 5/8x3/4 water meter like on your home. It is 98 to 100% accurate from 1/4 GPM to 25 GPM. It has a standard recording register on it so I will take monthly readings. I just couldn't spring for a electronic meter with that range, it was over $250.
I use two pressure gauges on my RO/DI system. One on the incoming and one after the carbon block so I know when filters are plugging. Here is a picture showing both:

http://i51.photobucket.com/albums/f369/AJOIII/2006_08_31020.jpg

[the other tang]

Nice, ok so it wan't an original idea. I assume you used plastic gauges, right? What brand and psi range? What differential do you look for in psi?

[SpectraPure]

hello-
thought I would chime in with a caution on using pressure drop for replacement determination on carbon block filters whne using our new filter ... our new ZetaZorb 0.2 micron sediment filter is an absolute filter and the pressure drop method is not particularly effective to determine the downstream carbon block life as the life of the downstream carbon filter is determined by VOC chloramine removal ability, not sediment plugging when protected by the absolute rated ZetaZorb. Thus, in our field testing we have seen the carbon blocks actually lasting their rated gallon capacity rather than being prematurely plugged up and requiring change because of pressure drop. In our testing with the effects of the ZetaZorb, the downstream carbon blocks were lasting twice as long as those same carbon blocks downstream of even the best 0.5 micron sediment filter. This is due to the ultrafine sediments that pass even the best 0.5 micron filter which plug up your downstream carbon filter long before its VOC and chloramine removal ability is actually consumed. The other benefit of actually testing your carbon block for actual species removal rather than by pressure drop is you prevent the species from passing on to your expensive RO membrane and DI section, whcih further improves the lifespan of those expensive components. Basically, your entire system is sometimes only as cost effective as the weakest component in the system.

[AZDesertRat]

As soon as I get the flow meter installed I plan to run the new ZetaZorb filter I just picked up from you and run the 0.5 micron carbon block until I start to see chlorine breakthrough. I will keep track or the water totals to see if I get the life out of the filters I hope to see.
No the gauges are metal. Brass or waterworks bronze is not a concern at all on the tap water or upstream side of the RO/DI. Its only after RO and especially DI that brass becomes a concern as the water is very agressive at that point and is trying to get back to its normal dirty state.

[the other tang]

AZ, do you have a pic of what chlorine breakthrough looks like. I have always changed mine out on a 6 mo schedule, but my water demand is up now. I have seen slight discoloration but nothing drastic, but that was right at 6 mo so I changed it.

[Randy Holmes-Farley]

I would not assume that you can see it.

[the other tang]

Maybe i misunderstood what AZ meant. He said " until i start to see chlorine breakthrough" Apparently he is testing the level, I took that as a visiable difference.

[Randy Holmes-Farley]

I think he means with a test kit, but I could be mistaken.

[the other tang]

Thanks, Randy. Do you test yours? What kit? I assume letting the carbon fail would mean premature membrane failure. I want to prevent this in any way possible.

[AZDesertRat]

Yes. Spectrapure sells a low range chlorine test kit for this purpose.

[the other tang]

Thanks Guys

[Randy Holmes-Farley]

My water company uses chloramine, and as part of data collection for this article, I tested for chlorine/chloramine:

Chloramine and the Reef Aquarium
http://www.reefkeeping.com/issues/2003-11/rhf/feature/index.php

After my RO/DI (and that of nearly everyone else), I detected none.