What is an acceptable TDS reading?

[puckerfactor]

Is there an opinion out there on what is an acceptable TDS reading for reef tank R/O D/I water? I just moved, and the R/O unit tipped over in the garage, breaking an elbow.....I replaced it, and purchased a TDS meter while I was at it. It currently is measuring 10ppm coming out of the product line. The house TDS measures 653ppm. I'm just not sure what threshhold people are using to indicate the need to replace the membrane and filters. (I must admit, I need to run more water through it and re-test, as it's been sitting for a while, and I'm not sure if the water I tested wasn't some of the existing water in the holding tank prior to moving)

thanks....

[Seahorsedreams]

For an RO/DI it should be zero. When I see 1 I start gathering up the supplies.

[CarmieJo]

I think the federal standard for distilled water is <10 TDS.

[wwest]

I have always had the rule of thumb is 10 or less. I think i will start flipping out at around 8.

I would let the R/O unit sit for awhile while flushinng and testing ever so often and then go from there.

[Seahorsedreams]

Hmmm.... strange. I've never heard it that way. I thought you measured the membrance function by monitoring it after setup and when you say an increase in values out of the RO portion before the DI unti it was an indication your membrance is on the way out. Like if you tap water is 320 the reading after just the RO should be 32 or less. (this value also depends on the rating of the membrane) When the number jumps your membrane is failing.

As far as water produced after the DI 0-1 is best. When it hits 1 I crawl under the sink and catch a look at the DI and it is indeed nearly spent. It's completely orange at 2 so I would not be able to accept any value higher than that unless I didn't mind water that was passing through a useless spent DI resin.

This is just what I understood......

Wait now, I we talking about just RO or RO/DI units here? I noticed Wes you didn't add the DI.

[Rob]

yes, anything under 10 is acceptable for our tanks..
as for measuring the life span on on our filters, yes, Renee is right, if you monitor after the RO stage and after the DI stage you can get a good idea of the filters status.

personally i flush my membrane on the first of each month.. simply flip the valve and let it run for 15 minutes and flip it back..

[PSH]

Depending on your RO/DI unit, you may be getting the best water you can. With your tap water TDS being so high. You may want to go with a higher rejection rate.

[puckerfactor]

Originally Posted by Rob

yes, anything under 10 is acceptable for our tanks..
as for measuring the life span on on our filters, yes, Renee is right, if you monitor after the RO stage and after the DI stage you can get a good idea of the filters status.

personally i flush my membrane on the first of each month.. simply flip the valve and let it run for 15 minutes and flip it back..

I'm not sure if my unit has a valve that can be flipped to flush the R/O membrane. A local supplier told me that the unit is designed to let a little water pass the membrane in such a way that it auto flushes it. I still like the idea of manually flushing it though...then you know it's done. I'll have to look at my options a little closer. BTW, great job on the podcasts...I really enjoy them. I'm so gald my wife got the ZUNE for me for christmas, in another few months, I'll be caught up on them!!!!

[Rob]

usually the lower output membranes have a higher rejection rate.
many "complaints" about the low cost "ebay" RO/DI filters is that they use cheap RO membranes. the fact is the 100 GPD membranes do have lower rejection rates, but aren't really less in quality.
besides if your output is 0 how much better can you get..

that said, if you have a 100 GPD membrane and you need better rejection you can try a 75 GPD to get better output..