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View Full Version : Is my TDS meter working?


Magickiwi
12-18-2013, 06:22 PM
I bought this product from reefsupplies.ca http://www.reefsupplies.ca/online-store/CSPDI-90GPD-w-Manual-Membrane-Flush-by-Spectrapure.html and it seems to be doing a pretty fair job of filtering water etc. It comes out odorless and tasteless. Testing for phosphate shows zero (my Hanna shows very tiny precense but the meter is extremely unreliable I find).

My perception is though that the TDS meter on the unit isn't working correctly. It displays zero TDS on the output but it also shows zero TDS on the input side of things. I'm dubious about if that is a reliable reading though. Most information I've seen estimates Calgary tap water as 160-600 TDS; including the city's own website. Is it measuring TDS AFTER the RO filter? Is that actually feasible to be zero TDS after an RO filter?

The Spectrapure instructions are extremely thin and they don't actually get into the nity-grity of how the unit works, what to look for etc. For example they don't say squat about the DI media. Is it color changing? What's the lifespan for it? Does an increase in the output TDS reading indicate it's time to change resins?

kien
12-18-2013, 06:51 PM
did you install the meter or was it already installed? Mine RO unit isn't spectrapure but looks identical. I got a 3rd party TDS meter (looks exactly the same as the one on yours) to hook up and the instructions told me to hook the "input" TDS leads inline with the output of the RO membrane. This can tell you if your membrane is going or not. I am currently reading a TDS of 3 out of my RO membrane.

Magickiwi
12-18-2013, 07:19 PM
did you install the meter or was it already installed? Mine RO unit isn't spectrapure but looks identical. I got a 3rd party TDS meter (looks exactly the same as the one on yours) to hook up and the instructions told me to hook the "input" TDS leads inline with the output of the RO membrane. This can tell you if your membrane is going or not. I am currently reading a TDS of 3 out of my RO membrane.

It was pre-installed as was the membrane flush (which I use pretty regularly). I've only made probably a few hundred gallons since I set the unit up so I guess it's possible the membrane and sediment/carbon filters are doing a good enough job to give me 0 TDS as an output.

I also found a more extensive manual for the model I have on the Spectrapure website. I only received a three or four page guide which didn't have details in it, only set up instructions. This manual says if I get anything but a zero on the output from the DI it's time to change my DI cartridge and my waste water/clean water ratio should be 4:1 and if it's lower then I need to replace my unit.

Sure helps when I get the whole instructions huh?

lastlight
12-18-2013, 08:12 PM
i have at times with a new membrane gotten zero readings for a while (after the unit had been running for many hours). I typically wait till I get a reading of 2 or 3 before passing the water through the di. after hours of running i will often check the IN reading and it's 1.

So your unit may be ok.

kien
12-18-2013, 08:13 PM
So your unit may be ok.

teehee...

mike31154
12-18-2013, 09:29 PM
Looks like an HM DM-1 dual TDS meter which is what most assemblers of RODI systems offer. They're factory calibrated with NaCl solution, so should be good out of the box. I would however be somewhat suspicious of a 0 TDS reading after the RO membrane particularly right after starting the system up. My tap TDS is around 184 & it takes a few minutes after start up for it to settle down to 1 TDS after RO.

Sediment filters do little or nothing to lower TDS, they're designed to trap solids, not dissolved solids. I installed a second TDS meter on my system to monitor the tap water TDS vs TDS after my two sediment filters & the carbon stage. Shortly after I put pressure to the system, the TDS after those 3 stages (before the RO) is actually higher than the tap water reading to the tune of up to +20. I presume this is due to stuff dissolving off the sediment filters during the days the system sits idle. Then when I put pressure to it, that stuff gets sent to the RO membrane. Takes a good 5 minutes for the reading after the pre-stages to drop below tap water TDS & it's usually only 1 or 2 TDS difference.

Might be worthwhile for you to double check where the probes for your meter are plumbed in. As a quick confirmation that it's working, you should also be able to pop both probes out of the JG fitting & stick them in tap water to see what you get for a reading. This will tell you how well it's calibrated, if there's a significant difference in readings between the two probes in tap water, you know you have an issue. And if you do remove the probes from the fittings, make sure you align them properly when you re install.

More info at their web site:

http://www.tdsmeter.com/products/dm1.html

lastlight
12-18-2013, 09:38 PM
yeah if it read that immediately upon startup there's no way. he didn't actually say how long he let the membrane filter for i don't think.

mike31154
12-18-2013, 09:45 PM
I also get 0 TDS out of the RO after running for about 4 gallons of product water, but that's only in the winter time when the water temperature going in to my system is below 10 Celsius. I stuck one of those cheap strip thermometers on to the first stage cartridge housing. Best I can get in the summer is 1 TDS out of the RO. That's also why I tend to make at least 5 gallons of RO water before switching over to making DI.

Magickiwi
12-19-2013, 12:51 AM
So your unit may be ok.

That's what she said! BOOM! I had to go there.

Thanks for the advice guys, your info and the longer manual from spectrapure cleared it up a bunch for me.