RO Unit Problem

[percula99]

I have a Kent Marine RO24TFC (25GPD) unit for producing RO water for my 180 reef tank. I have used it for several years with no problems.  I wanted to change the membrane and filters and upgrade the unit to 50 GPD. I just bought a new MTFC50 membrane, a 1 micron sediment filter, a matrix carbon filter and a 50 GPD flow restrictor from an online service. When I installed the new components my inline TDS meter read over 400 but it quickly started to decrease as I flushed the unit. I got it down to a reading of 4 TDS and left it running normally overnight hoping to get it down to 0 TDS so I could start using my RO water. This morning the reading has gone from 4 up to 8. Instead of going down, the TDS is rising. I double checked everything and it all seems to be installed properly. What could be the problem?

Thanks in advance for any assistance you can provide.

[Shrimpy]

RO membranes are meant to give you a TDS of less than or equal to 1/10th of the TDS of your incoming water. For example, TDS of your feed water is 250 ppm, your RO water should be 25ppm or less. If the TDS is higher than 1/10th of the TDS of the feed water the membrane needs replacement.

You mentioned you have had this unit for years. When was the last time you had your TDS meter calibrated? Has it ever been calibrated? It should be done once a year minimum.

[Shrimpy]

This too...

If you are testing a new unit, always wait until it has run for a few days before testing. It takes quite some time for the newness to wear off the system. The meter can "see" particles that your eye can't and you'll get an unreliable reading unless you allow the unit to break in.

If you are servicing the unit, take your test before changing the carbon filters. New carbon filters will corrupt the reading considerably and read much too high. The meter can "see" the manufacturing residue from the carbon filters.