Good or bad?

**Allowin** · 05-24-2009, 06:51 PM

Give me some thoughts about this.

HM DM-1 Inline Dual TDS Meter ppm/RO/DI /Aquarium - eBay (item 370118156563 end time Jun-20-09 21:03:19 PDT)

**CarmieJo** · 05-25-2009, 12:01 AM

I think it is fine. It is nice to have the pre and post filter readings easily available.

**Iron E** · 05-25-2009, 05:11 PM

Looks like a good deal. I've seen them for $20 more in several on line stores. I was thinking about one myself. Being able to see the in/out difference will alert you to the need to change out filters.

Tom

**Phurst** · 05-26-2009, 10:10 AM

I've got one. No problems 2 years in.

**KAN** · 05-28-2009, 03:16 PM

I got one. Had for little over a year now. wish I got another just might

**AZDesertRat** · 06-15-2009, 01:06 PM

I have two of these myself.

Thumbs down if you want accuracy. They are not temperature compensated and actually sense air temperature and not water temperature which can be significantly different.
(I have seen the probe cut apart, the temp sensor is inside the fat part behind the small rectangular hole in the exterior plastic. It does not see any water just air, the readings can be off like 2 ppm for every degree C the air and water are different which can make Ro and DI readings significantly off)

They also cannot be used portable so you lose the flexibility of a handheld TDS meter. To troubleshoot or even calculate a RO/DI units rejection rate and final TDS you need 3 TDS points not two. Tap water TDS, RO only TDS and RO/DI TDS. With the dual inline you only get two out of the three, normally RO only TDs and RO/DI TDS but not tap water TDS.

On the other hand I use them as a rough guide as to membrane and DI condition since all it takes is the push of a button and flick of a switch. They never ever agree with my HM Digital COM-100 handheld meter which is temperature compensated but they are not the same quality either.

I would highly recommend the COM-100, same manufacturer but a much better meter. It gives you accuracy and portability, you can test the tap water, RO water, RO/DI, storage container, grocery store bottled water, water & ice store RO water, the neighbors, your buddies, the LFS etc all with one meter.

**CarmieJo** · 06-15-2009, 01:39 PM

Hi AJ and

to TR. Thanks for this useful post.

**AZDesertRat** · 06-15-2009, 02:17 PM

Glad I found this forum. I was on RC for about 7 years and 17,000 posts and was a member of team RC before they decided the didn't want me around anymore when i pointed out one of their vendors was not telling the whole story. I guess the almighty dollar was worth more than the truth even though it could steer some of their members in the wrong direction!

**Phurst** · 06-15-2009, 02:54 PM

Well, we're certainly glad to have you. Always nice to have people around with years of experience. Sorry to hear RC put a bad taste in your mouth, but you're not alone there...

**CarmieJo** · 06-15-2009, 03:27 PM

LOL, sounds like they could be taking a tip from some or the LFS's we've all heard about. "That cute little blue tang, yeah, it'll be just fine in your nano!"

Originally Posted by AZDesertRat

Glad I found this forum. I was on RC for about 7 years and 17,000 posts and was a member of team RC before they decided the didn't want me around anymore when i pointed out one of their vendors was not telling the whole story. I guess the almighty dollar was worth more than the truth even though it could steer some of their members in the wrong direction!