TDS Meter/Calibration

[SSalty]

I just received my HM Digital COM-100 TDS meter. Is it neccesary to buy the calibration solution to calibrate the meter?

I understand how to use the meter but am confused about the calibration.

Thanks.

Oops, forgot to mention. Right when I took it out of the box I tested my tap water and it read 230ppm, then I tested my R.O and it read 12ppm. Isn't this a little high? Or is it because its not calibrated correctly?

[dragon_slayer]

Originally posted by SSalty
.......... I calibrated my tap water and ........ then I calibrated my R.O .............

do you mean you tested them?

kc

[SSalty]

Originally posted by dragon_slayer
do you mean you tested them?

kc

oops, post edited.

[dragon_slayer]

Much better. Most meters are calibrated when you receive them, 12 out of your membrane is excessively high how old is the membrane? what is the reading out of your DI cart?

kc

[AZDesertRat]

If you keep it cleaned with DI water after every test and keep the cap on it it should not require calibration for a long time. Don't let it sit and the probe dry out after testing tap or even RO water. I make it a habit to triple rinse with DI after each and every test so I don't forget. Also don't test salt water, its over the 10,000 scale.
What membrane do you have? If its a 100 GPD Dow then 12 is not bad but if its a 75 GPD Dow or a GE or Applied then its a tad high. You should be seeing a rejection rate of +/- 98% if its a 75 GPD and is in good condition, 90% if its a Dow 100 GPD and somewhere around 96 to 98% for the others.
You also need to let water run for awhile and stabilize. When membranes first start producing water they have what is called "TDS Creep" meaning they start out high and gradually drop down into the proper range. Same goes for DI, but it will drop much more quickly.
Great choice on a meter by the way, that's the best one you can buy.

[SSalty]

Originally posted by AZDesertRat
If you keep it cleaned with DI water after every test and keep the cap on it it should not require calibration for a long time. Don't let it sit and the probe dry out after testing tap or even RO water. I make it a habit to triple rinse with DI after each and every test so I don't forget. Also don't test salt water, its over the 10,000 scale.
What membrane do you have? If its a 100 GPD Dow then 12 is not bad but if its a 75 GPD Dow or a GE or Applied then its a tad high. You should be seeing a rejection rate of +/- 98% if its a 75 GPD and is in good condition, 90% if its a Dow 100 GPD and somewhere around 96 to 98% for the others.
You also need to let water run for awhile and stabilize. When membranes first start producing water they have what is called "TDS Creep" meaning they start out high and gradually drop down into the proper range. Same goes for DI, but it will drop much more quickly.
Great choice on a meter by the way, that's the best one you can buy.

I don't know what membrane I have. Can you add a 100 or a 75 GPD down membrane to all Brands of R.O units or do they only fit in certain types of R.O units? The R.O unit that I have is a Microline. The R.O filters/membrane is about 6 months old, and I use quit a bit of water. Maybe is it time to change the filters?

Also, I have (2) 2 gallon inline R.O holding tanks, is this bad?

By DI, do you mean Deionized water or Distilled? I don't have access to Deionized water to clean the probe, however, I have been concidering adding a deionizor. Would this be a good idea?

Basically I have no idea by what you said about the GPD dow. If you could clear these things up it would be great.

Thanks

[dragon_slayer]

Originally posted by SSalty
..........I don't have access to Deionized water.........however, I have been concidering adding a deionizor. Would this be a good idea?

Yes you should always use a DI (Deionized) as the last stage of your filtering before adding to the tank, it should take your TDS down to 0.

on the GPD, the lower your GPD the higher the rejection rate in most cases and the lower the TDS coming out of the membrane. some people think the holding tank is a bad idea some do not, i am one of those who uses one, a 30g one. i store only RO water and it passes through the DI on its way to the tank. i also have a RO spout on my kitchen sink for drinking/cooking water. the TDS from my tap is average 300, out of my 100 GPD membrane it's 4, out of the holding tank it's always 4 and out of the DI 0, and i replace the DI when it gets to 3.

kc

[SSalty]

....

[SSalty]

I also have a spout on my kitchen sink for R.O drinking water, but isn't it bad to drink DI water? That's the only thing that would steer me away from getting a DI.

So would it be best to get a 100 GPD or a 75? Which one would be better if I decide not to go with a DI?

[dragon_slayer]

you don't drink the DI, you simply put a T in the line between the RO and the holding tank for the drinking water spout, then a line out of the holding tank to the DI to the tank, the tank is the only thing that gets DI water.

on the GPD what are your demands? get a unit that will keep up with your demands, i used to have a 50 GPD and it was producing 24/7 and couldn't keep up. now i have a 100 GPD and it does a great job.

kc

[AZDesertRat]

The 75 GPD Dow Filmtec or a 90 GPD Spectrapure SpectraSelect series would be you best bet if you do not want to use DI. There is no reson not to use DI though. I also use my unit for drinking water as others have said. I pass water through the dual membrane RO system into a 14 gallon pressure tank so I store only RO water for drinking and ice maker. From the presure tank it can then go to the RO faucets in my kitchen and garage laundry sink, to the ice maker and to my MaxCap DI system for tank water.
There is not hard medical evidence stating drinking DI water is bad for you. It does taste very bland and is not refreshing though so you wouldn't normally drink it by choice but lots of people do. Companies like Spectrapure actually make a remineralization cartridge so you can add specific minerals back to the DI and it makes fantastic tasting coffee. If you have ever visited one of the nationally known name brand coffee houses whose name I don't need to mention, you have drank DI water that has been remineralized using this system.