TDS Testing

[DewaynelovesAbby]

I purchased a Home/Reef unit from AWI a couple weeks ago and am at my wits end on how to test the TDS. AWI assures me that the TDS will be at Zero on the DI side. However, I get the same basic reading on both the RO and the DI. I got a permeate pump and installed it last night and also replaced the Horizontal DI cartridge. But I still get 15 PPM on the RO and around 20 on the DI. I have a new tester that I am using. It is a HM Digital TDS-3. Any thoughts? Thanks.

[Texreefer]

A new cartride will test high for a good 20 minutes of use, you need to let a new system run for a bit before it flushes averything out.. also might find something known to have zero TDS and just double check your tester.

[DewaynelovesAbby]

Does it matter whether the pressure tank is on or off?
Is the fast flush supposed to be open or closed?

[DewaynelovesAbby]

Would distilled water have a Zero TDS?

[DewaynelovesAbby]

One other question; is it normal for the permeate pump to come on and off and the water to surge slightly while the water is running? I understand that the pump isn't really coming on and off, since it isn't powered. But you can hear it every few seconds then the water spurts. Thanks.

[DewaynelovesAbby]

I got some distilled water from the store and it reads zero with the tester. I let the DI run while we were gone this AM for over an hour and the tests still come to 14-15 on both the RO and DI. I wonder now if this means they sent me another bad DI cartdridge?

[CoryDude]

Could be a dumb question. Have you checked to make sure the DI cartridge isn't installed up-side-down? I know Russ at Buckeye had a similar situation as yours:

http://www.maast.org/forums/showthread.php?t=42730

[Bill S]

If you have a pressure tank, your TDS will never be zero. Ask Russ at Buckeye. The backpressure allows a bit of leakage. Same thing happens when the unit cycles on and off.

[DewaynelovesAbby]

Will you not get zero if you turn off the valve to the pressure tank?

[Bill S]

Yes, if you fill from the RO/DI unit with the pressure tank off, you will get zero. HOWEVER, it will take a bit of running to get there. There is always some bleedthru of the membrane when it is shut off. That's why they don't recommend running directly from an RO/DI unit to a tank float valve. It cycles the RO/DI unit too much. Not only that, but it encourages a flood...