TDS interpretation

[seahorsedreams]

On found this equation online for evaluating RO/DI function with a TDS monitor. Is this equation right?
If purified water divided by tap water is greater than 0.2 then it is time to change the membrane.
Renee

[tendar]

Are you testing the water out of the DI end or the Membrane end? I am not for sure about any equations though. My tap watter runs in the 600-800ppm range varying weekly so go through membranes about every 6 months. Once mine hits around 50 out of the RO membrane I change it.

[seahorsedreams]

I test the water after all the filtration just before it hits the ole storage bucket. Yikes! Is this wrong?
Renee

[David Grigor]

NO not wrong just depends on what your testing for. Testing at the final output and getting a high reading it could be the RO membrane needs to be replaced or most like the DI.

When you suspect the RO or getting near the end of the life then test before the DI......

My general rule of thumb is a TDS reading of about 30 before switching out DI.

If your dosing Kalk in your topoff the reading can be even higher because the Kalk will precipitate any phosphates from you top off water before it reaches the tank....

[DaveC]

I just recently purchased a hand held TDS meter and I tested my water after the RO/Di and it measured 274ppm..WOW...I thought there was something a matter with the tester..I did the calibration by the way...I then tested my faucet water and it read 170..100ppm less than after the filter...problem was I was not back flushing my membrane enough...after back flushing for at least an hour my tds after the RO/DI read 8ppm...happy once again...but to get back to the question..I also was not sure what it is suppose to read...I thought I read or heard 90 percent less than your faucet level?? is this right, is there any set equation?? I am guess becuase my tds was so high that is why my tank developed some red slim...also does anyone know would this affect the micro algea in a refugium...mine has continued to sort of deteriote lately,,could it have something to do with high tds??

DaveC

[seahorsedreams]

My final output reading went from 0 to 10. I changed the sediment and DI filter and it went back to 0. (The DI was exhausted). Is it okay to assume the RO is still filtering fine? I've learned not to assume anything on my own in this hobby and that nothing is as simple as you think it should be.
Renee /ubbthreads/images/graemlins/moron.gif

[Chuck S]

If your TDS reads 10 without a DI and just RO your still fine. RO does not remove all levels like posted above. I try not to get too worked up over the numbers yet by the look of my inhabitants. I regularly have levels between 0 and 10PPM. It all depends on level my DI has been exhausted. I have a 5 stage unit so I utilize a double DI. Levels usually test 0 but as things exhaust a bit it raises. I usually replace on DI at a time.

[brody98]

what testers are you guys using? I just got a Milwaukee T74 tds tester from foster & smith it was kind of hard to cal and get it to hold the same number each time I put in the cal fluid, mine is probably a piece of junk, but which ones are considered "good ones" and where do you get them from?