View Full Version : Does anyone have a DI meter built into their RO/DI?

01-03-2013, 03:35 AM
As my tap water quality is poor and the RO/DI still measures high in phosphates and DS, I was wondering if purchasing a unit with a meter built right into it would be useful or would it, as always, need to be recalibrated regularly thereby eliminating the convenience. Anyone with experience?

01-03-2013, 03:44 AM
you can add a tds meter to your system.
do you use colour changing DI rsesin?

FragIt Dan
01-03-2013, 03:47 AM
Are you talking about a TDS meter? I don't know of anything that will measure ions in general. If you still have phosphate post DI, slow the water flow down or change the DI as it may be exhausted. DI works based on exposure time, so if you have a reservoir you need to put it after the DI and put a one way valve in between the DI and the reservoir. Used properly, you should be phosphate free.

01-03-2013, 03:53 AM
Are you on a well?

01-03-2013, 04:06 AM
Are you talking about a TDS meter?

Yes, that darn T didn't stick. TDS.

And I currently do not have a RO/DI unit but after testing the levels from the towns' RO/DI retailers, the best system is still high in phosphates and TDS. Unfortunately, I tested AFTER I got the cyano and ha breakout. So, a shopping I will go because you know there isn't anything more sexy than a great RO/DI unit. *heavily dripping with sarcasm*

So, looking at all of the upgrades that I need to do to my system, it seems that if I can go sumpless and skimmerless but have a great input of water on an every odd day basis, the RO/DI unit may be my best bang for buck. So looking at units on ebay, I'm wondering if the built in meters are worth the extra coin vs the benefit.

01-03-2013, 04:40 AM
I'm wondering if the built in meters are worth the extra coin vs the benefit.
An inline TDS meter is invaluable. Dual is nice for measuring both source and post-filtered water
Inline gives you the option of monitoring your filter media and checking output before you fill your storage container

Hanna makes a great dual inline that sells for $30 from BRS (http://www.bulkreefsupply.com/dual-inline-tds-meter-dm-1-hm-digital.html) and $36 from J&L (http://www.jlaquatics.com/product/ro-aftdsi/HM+Digital+Inline+TDS+Meter.html)

Buy a bottle of cal solution (http://www.bulkreefsupply.com/tds-342-calibration-solution.html) and check it once a year, or when you suspect it could be off

01-03-2013, 06:33 AM
IMO, if it's included, fine, but I wouldn't pay extra for it. Any meter will need calibration at some point. With properly maintained pre filters, flushing your RO membrane and running DI resin that indicates exhaustion with a color change, you'd be good for years. If the TDS meter is going to give you peace of mind, fine, but it's money you could put towards something else.

01-03-2013, 08:13 AM
I recently added a Dual Inline TDS meter to my system (previously using just a hand-held). I placed the two points after the RO membrane, and then after the DI.

The pre-filters don't really do much for TDS (which is measurement of much much smaller particles), leaving the membrane and DI resin doing the brunt of the work... Since DI resin is costly, knowing how efficient my RO membrane is operating is very important! I now can do a more serious flush of the membrane when the TDS post-RO is >5 TDS... and with the dual meter, I can quickly (seconds) have peace of mind that the post-DI water is still 0 TDS.

Using a hand-held checker getting measurements from the post-RO/pre-DI water is still totally possible - though somewhat tricky... It would take a Tee, check valve, and manual shutoff valve, letting you divert some water from the post-RO/pre-DI stream... you would need the check valve between the Tee and the DI though to ensure you don't get back-flush water from the DI into your Tee causing your reading to be skewed.

01-03-2013, 08:29 AM
I should have elaborated on my setup
I have both a single and a dual meter
I measure supply water, post RO and post DI
FYI, I also have pressure guages on my supply and pre-RO to monitor the filters. You could say I'm a bit OCD

For the OP, as Brad stated, if it's included and is comparable to what I linked above, go for it

I only mentioned what I use as I like to keep an eye on most stages of my system

01-03-2013, 02:04 PM
I like an inline TDS meter in one place - between the RO membrane and the DI resin so that I know how much TDS is going to the DI. This is a luxury though, and not needed. I like to use a handheld meter for product water. Make sure that any TDS meter that you buy is either self-calibrating when you dip it in calibration solution or it has manual calibration. All TDS meters are "factory calibrated" but do not buy a TDS meter that you can't calibrate afterwards because the calibration will wander off.

IF you buy a dual TDS meter, spend the extra few bucks to get the HM Digital DM2 as it has dual calibration where the DM1 has only one calibration screw for both probes which often do not read the same, so it is impossible to calibrate both probes properly. Or make sure whichever brand it is that if it has dual probes it also has dual calibration. The ones Greg linked to above are both the DM1.

I have fond that I can't rely solely on the color of color changing DI resin because I found the outside of the DI resin would all change color and I would dump it out to find the core of the DI resin still had plenty of color! So now when the color on the outside is all changed that's my red flag and I start testing product water until it shows 1 ppm, and then I change the DI resin. In my case, the DI resin often last another 4 months or so after the outside portion has changed color.

What is the TDS of your tap water? Phosphate level? Chlorine/chloramines?

01-03-2013, 02:21 PM
HM Digital DM2 as it has dual calibration where the DM1 has only one calibration screw for both probes which often do not read the same
Mindy, have you some more info on this ?
I'd like to know if I'm looking forward to some kind of failure :surprise:
I currently own the DM-1 and the SM-1

01-03-2013, 02:27 PM
What info do you want? Google for owner's manual for the DM2 to compare. Have you tried calibrating yours yet? Put both probes into the same glass of tap water and see if they read the same. If they do you're lucky (for now), if they don't read the same then there is nothing you can do to get them to read the same. Then you need to set the lower reading one to the calibration solution (usually 342 ppm), and if the second one then reads 3 ppm higher you just have to remember that 3 ppm on the second one means "0". That's about all you can do.

01-03-2013, 02:30 PM
I wasn't expecting to hear issues

I've never had to cal mine since I bought them
Looks like I'll have some fun to deal with in the near future ...

Oh, and thanks for the info :smile:

01-03-2013, 02:38 PM
Thanks again Mindy for the info
Every day there is something to learn about
Sucks that it's about my own gear :wink:

Reef Pilot
01-03-2013, 02:51 PM
I have a dual TDS meter, one shows after RO and before DI, and the other shows after DI. When the RO tds starts to go up, it tells me it is time to flush the membrane. My final RO/DI water is normally 0 or 1. When it goes up it is time to change DI. When flow slows down, it is time to change the sediment and carbon filters.

01-03-2013, 02:57 PM
Pretty much what I was trying to say about TDS meter locations

Do you have a pressure gauge ?

01-03-2013, 02:58 PM
I've never had to cal mine since I bought them

What do you mean you've never had to? How long have you had the meter? You should calibrate every 3-6 months.

Reef Pilot
01-03-2013, 03:03 PM
Pretty much what I was trying to say

Do you have a pressure gauge ?
I have a pressure gauge on the input source side only, which is my house pressure, and it is normally around 70.

01-03-2013, 04:04 PM
What do you mean you've never had to? How long have you had the meter? You should calibrate every 3-6 months.
I calibrated them when I set the unit up in May, so I guess I'm due for another cal session
I thought they were good for a year :rolleyes:

01-03-2013, 04:05 PM
I have a pressure gauge on the input source side only, which is my house pressure, and it is normally around 70.
My input pressure is around 60psi
My pre-RO pressure (post sediment and carbon filter) is the same, but when it dropped below 50 this last fall, I replaced my sediment filter and all was good again

01-03-2013, 07:32 PM
You can go a year between calibration if you want, whatever works for you.

01-03-2013, 09:31 PM
My system included a DM-1 Dual TDS meter & I haven't calibrated it in the over 3 years the system's been running. These aren't lab grade instruments, although I think the DM-1 accuracy is +-2% which is actually pretty good. Not sure how a +-2% shift in accuracy relates to the displayed TDS, but I would guess the meter read out isn't going to move until there are a few more % at work. We're making up water for a hobby here, not for medical purposes. Some folks still use treated tap water. It took 3 years until TDS out of my DI stage finally showed 1 instead of 0. Why would I attempt a calibration at this point & possibly risk messing it up? TDS meter is likely nothing more than a simple ohmeter calibrated to measure electrical current flow through water between 2 metal probes. If you don't mess with the probes, it's unlikely the calibration is going to change significantly. I've just read the calibration instructions for the DM-1 after finding a copy online & the word "may" is used with respect to the need for periodic calibration.

I can also attest to the fact that the colour changing DI media is a poor indicator of whether it's exhausted & pretty much a waste of money. You're better off paying less for the non colour changing DI media & putting the $$s towards a TDS meter if you don't have one. In addition to using TDS readings to monitor when DI media and/or RO membrane needs replacement, like gregzz, I use two pressure gauges to monitor when the pre filters need replacement. Not trying to say that calibration is never required, simply that it's best to know your own system, monitor the readings & if things are consistent, don't worry, be happy. If there's a spike or unusually low reading at a sample point where you expect some consistency, then it's an indication to investigate further & possibly look into calibrating. Calibration on some sort of calendar based schedule is of little value IMO.