19 ppm in topp off water is this that bad?

[Ben1]

After changing my DI resin about 1 month ago I am getting 19 ppm from my ro/di unit. I already ordered the replacement DI resin but how bad is it to let it get this high before replacement?

 

[Anonymous]

There's something wrong there. A DI cartridge should last a lot longer than a month with a well maintained RO in front of it. I have tap with about a 600 TDS reading (that's HIGH), and DIs last about three months here.

When did you last change your RO cartridges? What's the TDS coming out of the tap? What is the TDS coming out of the RO (before it hits the DI unit)?

It's not going to kill your reef or anything for now, but you shouldn't let it get that high again.

 

[GSchiemer]

It really depends upon the starting TDS number. If your input water is at 1900 ppm, then 19 is a good number since it shows a rejection ratio of 99%. Having said that, 19ppm TDS is a relatively high number, especially if you took this measurement after the DI filter. To answer your question, yes, it is "bad" to let the number climb that high. The TDS reading out of my DI filter is less than 1 TDS. I'd also check the rejection ratio of the RO membrane. It may be bad as well.
Greg

 

[Anonymous]

These two people wants to get the root of the problem solved, instead of answer your question directly. I also feel that you need to find out what is the problem of the filter output, instead of just buying replacement DI again, again, and again.

>...how bad is it to let it get this high before replacement?

Addressing you concern, I will answer you this way: It really depends on what are those 19ppm. If it is 17ppm Ca, and 2ppm Mg, then you have nothing to worry about. However, it is most likely that it is not the case, and you really need to get the issue solved before you end up with a bad algae problem, or livestock dying without appearant reason. Doing regular water change will help you buy some time.

Let us know if you want anybody help you out in RO/DI trouble shooting... most likely, you will need to borrow a TDS meter....

 

[Ben1]

Yeah, I replaced the membrane less then 3-4 months ago. The TDS from the tap is close to 500 ppm. After the RO it is around 23 and after DI it is usually around 2. I have neer been able to get the 0 reading. I am wondering if I need to replace all the RO tubing on the unit. Maybe it has some build up in it or in the auto shut off valve.

I have never had a DI cartridge last longer the 1 1/2 months to 2 months max. I use it for top off and about 100 gallons of water for changes a month.

 

[mark78]

Are you using the first gallon or so of water the unit is making? Has anything changed since you were getting the 2 tds? Is the container your filling to test possibly giving it a TDS? I know when I fill a cup for my water tests, the first cup I get is usually around 20tds, after the first rinse I will get a 0 TDS reading.

My tap water is 300-400ppm though may be going up with summer.